librarian2003 (librarian2003) wrote in weagardening, @ 2010-12-07 01:13:00 |
|
|||
Current mood: | cold |
Entry tags: | hybrid musk roses, hybrid perpetual roses, noisette roses, plant vascular systems |
Week 9
This weeks topics are Noisette, Hybrid Perpetual and Hybrid Musk Roses; and the main topic is Plant Vascular Systems.
The handout for this week's roses is here:
GARDENING FOR PLEASURE
Plant of the Week : Roses
Noisettes, Hybrid Perpetuals and Hybrid Musks
1 Noisette
The Noisette group are derived from a cross between Rosa moschata and 'Old Blush China ' made by John Champneys of Charleston, S. Carolina, in about 1802. Seedlings from the resulting hybrid were raised by a Charleston nurseryman Philippe Noisette and sent to France where they were developed. One, which flowered repeatedly, was named 'Blush Noisette' and when crossed with Parks' yellow china produced the yellow Tea Roses and also the Tea Noisettes.
They are free-flowering and although some are not totally hardy, there are varieties that are very hardy and will thrive in bad conditions such as inferior soil, shading or even a north facing position.
Cultivars
‘Aimée Vibert’ (‘Bouquet de la Mariée’, ‘Nivea’) Small clusters of double, pure white, gently perfumed, medium sized blooms. A vigorous climber with near thornless wood. 12 x 10' VIBERT France 1828
‘Alister Stella Gray’ (‘Golden Rambler’) Yellow with stronger tones at the centre, paling with age to cream, well perfumed. Flowers are produced generously and repeat throughout the season. Few thorns. 15 x 10' A.H. GRAY UK 1894
‘Belle Vichyssoise’ Generous bunches of small double soft pink flowers with a slight fragrance. 15 x 8' LEVEQUE France 1897
‘Blush Noisette’ One of the most useful of the Noisettes, always in flower during its long season that extends into the autumn. Can be grown as a shrub or left to tumble. Semi double blooms are small and bunched together in clusters. 7 x 4' NOISETTE USA 1825
‘Céline Forestier’ Large scented flowers of lemon to pale primrose. Flowers appear regularly throughout the summer, often into autumn, and are generously perfumed.
8 x 4' TROUILLARD France 1842
‘Champney's Pink Cluster’ One of the first of this group to be introduced. Highly perfumed double soft pink flowers tinged with deeper pink shades are produced in large clusters. 15 x 8' CHAMPNEYS USA 1802.
‘Claire Jacquier’ Climbing rose with medium sized, rich yellow blooms that are double and perfumed. 15 x 8' BERNAIX France 1888
‘Crépuscule’ Double flowers of orange and apricot. They start out from pointed buds but end up loose and almost shaggy. Gently perfumed. Not too many thorns.
3.5 x 1.5m 12 x 5' DUBREUIL France 1904
‘Duchesse d'Auerstädt’ Scented flowers are copper yellow to apricot, very full, quartered and highly perfumed. 10 x 8' BERNAIX France 1888
‘Mme. Alfred Carrière’ A famous and beautiful rose. Blooms in clusters of double, white flushed powder pink, are very fragrant, produced in abundance all summer long. Good on a North wall and also tolerant of poor soils and shade. 15 x 10' J. SCHWARTZ France 1879.
2 Hybrid Perpetual
Hybrid Perpetuals are a mixture of Bourbons, Portlands and other existing groups, bred to produce large, full flowers on robust plants. They are very vigorous and in late summer produce tall new shoots which, when pegged down, flower along their entire length in the following season. These roses were at their height of popularity in the Victorian era when big was considered to be best and indeed most of them are sumptuously well endowed with big blooms and equally big perfumes. They are not, as the name implies, totally perpetual but most will provide at least one second flush, some are more frequent if only with odd blooms.
They vary in size, there are varieties suitable for pots and some that can be grown as climbers.
Hybrid Perpetuals crossed with Tea Roses formed the Hybrid Tea group.
Cultivars
‘Alfred Colomb’ Very double, dark red to crimson with various other flecks of pink and carmine, paler on the petal reverse. Very fragrant. 4 x 3' LACHARME France 1871
‘Anna de Diesbach’ (‘Gloire de Paris’) An upright and tall rose, very fragrant with over-sized blooms of deep, rose pink with deeper shadings. Its growth can be a little awkward. 4 x 3' LACHARME France 1858
‘Baronne Prévost’ Very double, flattish flowers of deep, rose pink. An upright and vigorous plant with ample foliage. Scented. Can succumb to blackspot. 5 x 4' DESPREZ France 1842
‘Baron de Bonstetten’ Somewhat cupped deep red flowers age as they mature when they bear shades of greyish purple. Fragrant. Upright, quite thorny. 4 x 3’ LIABAUD France 1871
‘Baron Girod de l'Ain’ Flowers cupped and full, bright crimson red with white edging to each wavy petal, fragrant and healthy. 4 x 3' REVERCHON France 1897
‘Baroness Rothschild’ Over-large very cupped flowers of soft rose pink, over a long period. Neat proportions. 4 x 3' PERNET PÈRE France 1868
‘Black Prince’ Fragrant, large cupped flowers of rich carmine shaded almost black. Vigorous. A slight tendency to mildew. 5 x 3' W. PAUL UK 1866
‘Charles Gater’ Clear red, globular, scented flowers on a vigorous upright plant with good foliage and prickly stems. Good in a tub. 4 x 2' W.PAUL UK 1893
‘Charles Lefèbvre’ From pointed buds emerge large, very full flowers of rich crimson shaded maroon. Very fragrant. Vigorous. 4 x 3' LACHARME France 1861
‘Comtesse Cècile de Chabrillant’ Shapely, cupped mid-pink flowers with a good perfume held erect on strong stems. Repeat flowering, can be grown in a pot. 4 x 4' MAREST France 1858
‘Countess of Oxford’(’Comtesse d’Oxforde’) Medium growing rose with light red, globular flowers and a good perfume. 4 x 3' GUILLOT PÈRE France 1869
‘Duke of Edinburgh’ Large, many-petalled shapely flowers of deep crimson red, scented and very free flowering. Good in a tub. 2 x 2' PAUL UK 1868
‘Duke of Wellington’ Shapely scarlet-crimson flowers, with deeper shades on the reverse of the petals, larger than average size on an erect, robust plant. Dislikes hot sun when its velvet textured petals become like brown paper. Scented. 4 x 3’ GRANGER France 1874.
‘Dupuy Jamain’ Very double, shapely flowers of cerise-red and considerable size with a heavy perfume. Happy in a pot and good for bringing inside as cut flower. 4 x 3' JAMAIN France 1868
‘Éclair’ A very dark red almost black bloom, with petals swirling to form a quartered pattern; highly scented. 4 x 3' LACHARME France 1833
‘Empereur du Maroc’ (Emperor of Marocco’) Very double crimson-tinged purple, highly fragrant and borne in heavy clusters. Can be lax in growth which is improved by regular pruning. Prickly stems. Can be marred by mildew and black spot. 4 x 3' GUINOISSEAU France 1858
‘Eugéne Fürst’ Large crimson purple flowers are quill edged and highly scented. They are borne on strong necks. 4 x 3' SOUPERT AND NOTTING Luxembourg 1875
‘Ferdinand de Lesseps’ A vigorous rose bearing shapely, flowers of Centifolia shape. Soft purple lavender shaded over-all with magenta. Scented. 4 x 3' VERDIER France 1869
‘Ferdinand Pichard’ One of the most attractive and well known of the striped varieties. Double, pink and crimson flowers striped and streaked, scented blooms are freely and repeatedly produced. 5 x 4' TANNE France 1921
‘Gloire Lyonnaise’ Large, cupped semi-double flowers of pure white with lemon at the base base. Nicely perfumed. 4 x 2' GUILLOT FILS France 1885
‘Henry Nevard’ Cupped, bright crimson flowers are large and sweetly fragrant. Dark green leathery leaves, bushy growth. Repeat flowering. 4 x 3' CANTS UK 1924
‘Horace Vernet’ Fragrant, high centred and shapely double blooms are rich crimson. Useful for a tub, also tolerant of poor soil. 4 x 3' GUILLOT FILS France 1866
‘Hugh Dickson’ A tall, rich red of distinction, with a lovely perfume, that because of a tendancy to be arching in habit is especially suited to the pegging-down principle, when it will produce an abundance of flowers. Good autumn display. Can also be used as a climber. 8 x 5' DICKSON UK 1905
‘John Hopper’ Bright pink and lilac, very double and sweetly perfumed blooms, sometimes deeper in colour at their centres. An upright and healthy plant. 4 x 3' WARD UK 1862
‘Juliet’ Deep yellow buds opening to expose rosy-red petals with yellow reverses. Repeat flowering. Slightly scented. 4 x 3' W. PAUL UK 1910
‘La Reine’ (‘Reine des Français’) Large, goblet shaped full blooms of silvery-rose pink from high centred buds. One of the first Hybrid Perpetuals introduced and a parent to many others. Fragrant. Continuous flowering. 3 x 2 LAFFAY France 1842
‘Mme. Victor Verdier’ Huge, very double light crimson to carmine blooms are blowsy, somewhat ruffled in style. Fragrant. 5 x 4' E. VERDIER France 1863
‘Magna Charta’ A sport of ‘Mme Gabriel Luizet’ this rose has flowers of bright pink with deeper, almost red shadings. Fully double and cupped until fully open. Scented and repeat flowering. 3 x 3' W.PAUL UK 1876.
‘Paul Neyron’ An outstanding rose not only in size of bloom but shape and colour, on the magenta side of rich pink with paler petal reverse. Very fragrant. 3 x 2' LEVET France 1869
‘Paul’s Early Blush’ (‘Mrs Harkness’) A sport of ‘Heinrich Schultheiss’ Huge, very double, highly scented flowers of pale pink to blush. Good in a tub. 4 x 3' W. PAUL UK 1893
‘Prince Camille de Rohan’ (‘La Rosière’). Blooms of huge proportion open from tubby buds to be flat topped very deep blackish-red, becoming deeper as they mature. 4 x 3' E. VERDIER France 1861.
‘Reine des Violettes’ The blooms are a rich shade of magenta purple to greyish mauve with a superb fragrance. They open very flat and quartered from plump buds and appear all summer. A large shrub. 5 x 3' 1860.
‘Roger Lambelin’ Similar to ‘Baron Girod de’ l’Ain’ in that the double blooms are maroon edged white. However this one needs extra care to achieve any garden worthiness. 4 x 3' SCHWARTZ France 1890
‘Souvenir d'Alphonse Lavallée’ Double flower combining many shades of crimson to purple maroon. Scented. Best grown as a small climber against a wall otherwise it will require support. 8 x 6' VERDIER France 1884
‘Vick’s Caprice’ Large, double cupped flowers with high centres, in pale pink and lilac with white and deep pink stripes. 4 x 3' VICK USA 1891
3 Hybrid Musk
Hybrid Musks were developed initially by the Reverend Joseph Pemberton of Essex in the early 1900's. He crossed ' Trier ' (descended from Rosa multiflora and a Tea Noisette) with Hybrid Teas to produce Pemberton Musks such as 'Cornelia' and 'Felicia'. By and large they were the first group of tidily proportioned roses to flower continuously. After his death, his work was continued by J.A. Bentall, while in Germany Wilhelm Kordes developed another race by crossing 'Trier ' with Dwarf Polyanthas to produce Kordes Musks such as 'Wilhelm' and its sport 'Will Scarlet'.
The flowers, usually borne in very large clusters, are not only attractive but usually sweetly scented.
Cultivars
‘Autumn Delight’ Semi-double flowers of soft to buff yellow from shapely buds in large trusses. Almost thornless, bushy growth. Fragrant and continuous flowering. Will accept poor soil and makes an attractive hedge. 4 x 4' BENTALL UK 1933
‘Ballerina’ A very well known rose. Large clusters of small single, pink blooms with a white centre. A prolific dainty and showy shrub. This rose is often produced as a standard with both the shrub and standard forms being extremely useful as options for growing in a tub. Will cope with shade and disadvantaged soil. Continuous flowering. 4 x 3' BENTALL UK 1937
‘Bishop Darlington’ A strong-growing neatly sized shrub, with large blowsy flowers, semi-double of cream with apricot, pink and yellow overtones, usually strongest at the centre. Strongly scented and profuse over a long period into the autumn. A rose that will cope with the more difficult areas of the garden even shade and bad soil. 5 x 5’ THOMAS USA 1926
‘Buff Beauty’ One of the most beautiful roses in this family of the rose. ‘Buff Beauty’ is known to often vary in colour between soil types bearing large trusses of anything from bright apricot-yellow to much softer buff-yellow flowers. Flowers are of medium size and semi-double. Nicely fragrant. Flowering from mid-summer onwards well into the autumn. If grown against a wall this cultivar makes an excellent smaller climber. Accepts most places in the garden. 5 x 5’ BENTALL UK 1939
‘Clytemnestra’ Sweetly scented flowers of a subtle shade of buff suffused with peach and salmon, with a bold coronet of golden yellow anthers. They are borne in clusters. Continuous flowering. 4 x 4’ PEMBERTON UK 1915
‘Cornelia’ Individually small, double, pompom like flowers of salmon pink with tinges of strawberry and salmon make up large clusters that sometimes cause the branches to bow under their weight. Free flowering over a long season and fragrant. Very good autumn flush. 5 x 5’ PEMBERTON UK 1925
‘Danaë’ Blooms of buff yellow fade to cream as they age, in large trusses on a vigorous healthy plant. Can be grown as a climber. Free flowering over a long period. 5 x 4’ PEMBERTON UK 1913
‘Daybreak’ A Pemberton rose. Medium sized trusses of semi-double lemon yellow to soft primrose blooms. Flowers well into the autumn. 4 x 3’ PEMBERTON UK 1918
‘Eva’ Large, almost single blooms of rich bright red to carmine, paling to almost white towards their centres. Scented, continuously flowering for a long season. 6 x 4’ KORDES Germany 1933
‘Felicia’ One of the more vigorous of the Hybrid Musks, matching its vigour in quantity of flower. Double silver-pink to salmon flowers, slightly muddled in style. Fragrant. 4 x 4' PEMBERTON UK 1928
‘Francesca’ The flowers of ‘Francesca’ are beautiful in a refined and understated way. Semi-double, medium sized, apricot yellow in large sprays on strong stems. The colour of this cultivar is rare. Scented. Continuous flowering. 4 x 4’ PEMBERTON UK 1921
‘Kathleen’ Flowers like apple blossom, in profusion. Large clusters of small, single flowers of blush pink with pronounced anthers borne on a long stem. Fragrant. A large shrub rose that could, given the support of a wall, provide good cover. 8 x 4' PEMBERTON UK 1922
‘Moonlight’ Another beautiful creation of Reverend Pemberton’s. Profuse semi-double flowers of lemon to white with pronounced stamens on long, often arching stems. A strong growing healthy plant. 5 x 4’ PEMBERTON UK 1913
‘Nur Mahal’ Large clusters of bright crimson, semi-double blooms held erect over strong stems. Scented. Can be used as a climber with support, even a pillar specimen. Continuous flowering. 5x 4' PEMBERTON UK 1923
‘Pax’ One of the most statuesque of the Hybrid Musks. Flowers up to 4". Very large cream fading to white blooms are borne in clusters on a vigorous shrub. Can be grown as a climber or alternatively makes a good, strong hedge. 6 x 5’ PEMBERTON UK 1918.
‘Penelope’ Semi-double, creamy-pink paling to white flowers, individual petals a little fimbriated, with a good fragrance. One of the most beautiful of the group with a very feminine delicacy to its porcelain like blooms. Continuous flowering. 5 x 4’ PEMBERTON UK 1924
‘Pink Prosperity’ Pink form of Prosperity with smaller flowers and denser growth. 4 x 4' BENTALL UK 1931
‘Prosperity’ Trusses of very double creamy-white flowers which look well against its dark glossy leaves, strongly scented. PEMBERTON UK 1919
‘Robin Hood’ Trusses of rich scarlet flowers, almost single. A tidy, bushy plant. Useful in a tub. Continuous flowering. 4 x 3’ PEMBERTON UK 1927
‘Thisbe’ Straw yellow rosette-like blooms in large clusters. Makes a successful hedge and is tolerant of all but really unkind positions in the garden. Continuous flowering. 4 x 4’ PEMBERTON UK 1918
‘Vanity’ Large clusters of big fragrant, almost lipstick pink, semi-double flowers on a vigorous bush. Recurrent bloom over a long season. 6 x 5' PEMBERTON UK 1920
‘Wilhelm’ (‘Skyrocket’) Clusters of crimson red, virtually single blooms. This is one of the few Hybrid Musks to provide a good display of hips in the autumn. Continuous flowering. Can also be considered a climber or at very least a pillar rose if given support. 5 x 4’ KORDES Germany 1944
Jo Hanslip
November 2010
Images are here:
Noisette, Hybrid Perpetual and Hybrid Musk Roses
The handout for Plant Vascular Systems is here:
GARDENING FOR PLEASURE
Plant Vascular Systems
Vascular plants (also known as tracheophytes or higher plants) are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms. Vascular tissue allows these plants to evolve to a larger size than non-vascular plants, which are restricted to relatively small sizes.
Non-vascular plants is a general term for those plants without a vascular system (xylem and phloem). Non-vascular plants include liverworts, mosses and hornworts.
Herbaceous stems
Herbaceous stems contain bundles of vascular tissues, held in place by the surrounding pith and cortex. The inner half of each vascular bundle consists of large, water-conducting cells of the xylem tissue; toward the outside are food-conducting phloem cells which are smaller in size. These vital tissues form pipelines of fluid transport, connecting leaves, stems and roots.
The most difficult tissue to identify in a stem is a single row of cells between xylem and phloem in each bundle. This same tissue also separates cortex and pith in the areas between bundles. This is the vascular cambium, a meristematic tissue whose cells divide laterally (towards the side), and so result in an increase in the stem’s diameter. Early in the development of many perennial species, activity of the vascular cambium changes their stems from herbaceous to woody structures.
Vascular bundles form ribs extending the length of an herbaceous stem, thus also functioning as supportive members, rather like steel rods in concrete pillars. But, the stem’s soft tissues of pith and cortex give great flexibility, allowing it to sway in the breeze without snapping. The arrangement of xylem and phloem in small bundles allows them to branch into leaves, and into branches of the shoot system.
Stem thickening
Compared to herbaceous plants, tree trunks achieve spectacular changes of magnitude because of the action of vascular cambium and cork cambium. The cork cambium is responsible for the formation of cork, the outer tissue of the tree’s bark.
When cells of the vascular bundle divide, they do so in three directions, resulting in three different types of cell.
New cells laid down on the inside of the cambium layer develop thick, lignified walls, and their protoplasm dies. They will become water-conducting cells of the xylem, known as wood cells.
When the vascular cambium divides outwards, it forms phloem cells. Many of these have thin walls, remain alive and conduct food; others develop thick walls and give physical support to the food-conducting tissue.
The third direction for division is sideways, to add more cells to the meristem as it increases its circumference around the growing core of wood.
Because inward divisions of the vascular cambium are more frequent than divisions outwards, a tree trunk’s wood is always thicker than the bark. When branches grow, they thicken in the same manner as the main trunk. The base of a branch becomes deeply buried in the trunk as woody tissues grow around it. Knots in timber are slices through these buried branches.
Maintenance of this continuity of tissue is essential in grafting. Alignment of the vascular tissues of stock and scion permits free exchange of water, nutrients and food while the tissues of the two parts fuse together.
The most recently formed wood, closest to the cambium, is called sapwood, and conducts water up the tree trunk. In the inner area, the heartwood, the cells are plugged with chemical substances and cellular debris. Metabolic activities in living cells inevitably create waste products. These are passed into the heartwood via vascular rays, narrow rows of cells that transport such substances.
The wood of many tree species has a pattern of concentric circles, annual growth rings. Vascular cambium suspends activity during autumn and winter when the tree becomes dormant, so ring growth only occurs during spring and summer. Each annual ring consists of several layers of large xylem cells, called springwood, followed by progressively smaller cells, the summerwood. To satisfy the demands of rapidly growing new foliage, larger cells in spring conduct more water, which is usually readily available and abundant in the soil in spring.
Monocots
In a typical monocot leaf, dozens, sometimes hundreds, of vascular bundles are scattered throughout the stem. The bundles are divided by uniform thin-walled cells rather than cortex and pith as in dicots. Because vascular and cork cambia are absent, there is no secondary growth leading to development of wood and bark. Trunk thickening in large monocots such as palms simply results from repeated formation of the scattered vascular bundle pattern. Compression and drying of outer cells create a hard crust that lacks the characteristics of cork. This lack of wooden rigidity helps trees such as palms to survive hurricane force winds.
The stems of other monocots are made even more supple by having hollow centres : bamboo and other grasses, for example, are supported by long, narrow thick-walled stems called fibres. At nodes inside the tube-like stems, the cavity is filled with reinforcing-plates to prevent buckling when the stems bend.
Roots
In roots, the vascular tissues occupy the centre of a root. They are surrounded by a layer of cells called the endodermis, whose function is to regulate the flow of water into the xylem. Immediately inside the endodermis is the pericycle, a row of cells from which branch roots arise, forcing their way through cortex. This arrangement allows the vascular tissue to be extended into the young rootlet.
Roots of older perennials thicken in much the same way as tree trunks. Vascular cambium lays down wood, and cork cambium produces cork. The presence of cork, with waxy suberin in its cells, greatly reduces the capacity for water uptake from the soil by older parts of the root. Most water enters a root in the young part close to the growing tip, notably in the root hair zone.
Leaves
After spending effort to channel water from the soil to its topmost branches, a plant must restrict water loss from the leaves, or face death from dehydration. The cuticle layer on the outer surface acts as a barrier to water. So do dense mats of epidermal hair. However, photosynthesis requires carbon dioxide from the atmosphere, and this enters via thousands of tiny pores, or stomata, usually on the lower epidermis.
Stomata may close on hot, dry days, in heavy winds, or when the soil becomes dry. At such time, photosynthesis may be slowed temporarily, but, when water loss exceeds the rate of uptake by the roots, it is more important that the plant curb the escape of water than manufacture food.
Phloem
Unlike xylem (which is composed primarily of dead cells), the phloem is composed of still-living cells that transport sap. The sap is a water-based solution, but rich in sugars made by the photosynthetic areas. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs. Organic molecules such as sugars, amino acids, certain hormones, and even messenger RNAs are transported in the phloem through sieve tube elements.
During the plant's growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant's many growing areas are sugar sinks. The movement in phloem is multidirectional, from source to sink, whereas, in xylem cells, it is unidirectional (upward).
After the growth period, when the meristems are dormant, the leaves are sources, and storage organs are sinks. Developing seed-bearing organs (such as fruit) are always sinks. Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.
Food-conducting cells are long, narrow cylinders arranged end-to-end in ranks. Their end walls are called sieve plates, and are pierced with holes. Threads of living cytoplasm pass from cell to cell through the sieve plates.
Phloem forms an ideal channel through which fungus mycelium can grow, as vascular tissue provides access to all parts of the plant. Injured phloem, therefore, rapidly responds with the formation of a substance called callose and a special protein that plugs sieve plate pores to seal broken sieve tubes near a wound. Meanwhile foods are diverted from the injured tissue to functioning phloem in adjacent areas.
Another isolating defence strategy entails discarding infected leaves. Even before an infected leaf separates from its stem, a tannin-containing cork layer forms across the leaf scar to secure it against the spread of micro-organisms.
Because phloem tubes sit on the outside of the xylem in most plants, a tree or other plant can be effectively killed by stripping away the bark in a ring on the trunk or stem. With the phloem destroyed, nutrients cannot reach the roots and the tree/plant will die. Stripping of bark round the entire stem by a plant predator is known as girdling. It can be done, within specific constraints, to fruit trees to reduce vigour and increase cropping.
Xylem
The xylem is responsible for the transport of water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. Two phenomena cause xylem sap to flow:
Transpirational pull: the most important cause of xylem sap flow is the evaporation of water from the leaves to the atmosphere. This transpiration causes negative pressure or tension in the xylem that pulls the water from the roots and soil.
Root pressure: If the contents of the root cells are more concentrated than fluid in the soil, water can move by osmosis into the root from the soil. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances, the sap will be forced from the leaf in a phenomenon known as guttation. Root pressure is highest in the morning before the stomata open and allow transpiration to begin.
Water-conducting cells are dead at maturity. In flowering plants, these have cylindrical shapes and relatively wide diameters. Both the end walls of the cells and their protoplasm are absent, so these vessels form continuous tubes supplying water to all parts of the plant, Their thickened, lignified side walls are perforated with numerous pits to permit the escape of water to living cells. In wood, pits allow water to be diverted into adjacent vessels should blockage occur.
Xylem appeared early in the history of terrestrial plant life. Fossil plants with anatomically preserved xylem are known from the Silurian (more than 400 million years ago), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks.
Useful web site:
http://www.emc.maricopa.edu/faculty/far
Jo Hanslip
November 2010
And images are here:
Plant Vascular Systems
I hope you enjoyed that little trip into the workings of plants.
Jo