GNETACEm. 



^3^ 



The Leaves of Cycadeae and Goniferae are covered by a firm epidermis, usually 

 strongly cuticularised, and furnished with numerous stomata, each with two guard-cells. 

 In the Gycadege the guard-cells are more or less deeply depressed, and the stomata occur 

 only on the under side of the lamina, and are either irregularly scattered, or arranged in 

 rows between the veins (Kraus). In the leaves of Conifers the guard-cells are also, 

 according to Hildebrand (Bot. Zeit. 1869, p. 149), always depressed in the epidermis; 

 and the stoma has hence always a vestibule. In Goniferae the stomata are developed 

 either on both or only on one side of the leaf ; when the leaf is broad, as in Dammara 

 and Salisburia, they are irregularly scattered ; when the leaves are acicular they mostly 

 lie in longitudinal rows ; and in the large leaves of Wehvitschia they are also arranged in 

 rows. The firm texture of the leaves of Gycadeae and Goniferae is due to a hypodermal 

 layer, often strongly developed, consisting of strongly-thickened, generally long, fibre-like 

 cells lying parallel to the surface ; in the leaf of Welivitschia 

 this hypoderma consists of spongy succulent tissue penetrated 

 by bundles of fibres, which acquires its hardness from a mass 

 of spicular cells. The chlorophyll-tissue of the leaves lies 

 beneath this layer, and is developed on the upper side of the 

 leaves of Gycadeae and of the broader leaves of Goniferae as 

 the so-called Pallisade-tissue ; /. e. its cells are elongated in a 

 direction vertical to the surface of the leaf and are densely 

 packed together. In Pinus, Larix, and Cedrus the cells which 

 contain chlorophyll exhibit the infoldings of the cell-wall 

 which have been already mentioned at p. 74. The middle 

 layer of the tissue of the leaf, in which also the fibro-vascular 

 bundles run, has usually a peculiar development in Gymno- 

 sperms ; in Gycadeae and Podocarpeae it consists of cells elon- 

 gated in a direction transverse to the axis of the leaf and to 

 the bundles, but parallel to the surface of the leaf, leaving 

 large intercellular spaces (Transfusion-Tissue of Mohl). In 

 the acicular leaves of the Abietineae the fibro-vascular bundle, 

 split into two, is enveloped by a colourless tissue, which is 



sharply diflferentiated from the surrounding chlorophyll-tissue (Fig. 102). It is paren- 

 chymatous, and is distinguished by the large number of bordered pits which the walls 

 of the cells bear (Fig. 356)^ 



FIG. 3S^.—Pinus Pinaster; 

 two cells of the colourless paren- 

 chyma surrounding the fibro-vas- 

 cular bundle of the leaf; t i the 

 bordered-pits cut across, f the 

 same seen from the surface. 



carpus, Dacrydium, Torreya, Tstiga, Cumiinghajnia. 3. No canals in the root ; canals in the cortical 

 parenchyma and in the pith of the stem : Salisburia. 4. A secretory canal in the root ; canals in the 

 cortical parenchyma of the stem: Cedrus, Abies, Pseudolarix. 5. Canals in the wood of the fibro- 

 vascular bundles of the root and stem ; canals in the cortical parenchyma of the stem : Pinus, Larix, 

 Picea, Psetidotsuga. 6. Canals in the liber of the fibro-vascular bundles of the root and of the stem ; 

 canals in the cortical parenchyma of the stem : Araucaria, Widdringtonia, Thuja, Cupressus, Biota, 

 In Cycadeae the canals are found disseminated through the cortical parenchyma of the stem ; the 

 pith of Cycas appears destitute of them. In their distribution they resemble therefore that which 

 occurs in the second class of Coniferse.] 



^ For further details see Mohl, Bot. Zeit. 187 1, Nos. i, 2. 



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