GNETACE2E. 
533 
The Leaves of Cycadeae and Coniferae are covered by a firm epidermis, usually 
strongly cuticularised, and furnished with numerous stomata, each with two guard-cells. 
In the Cycadeae 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 Coniferae the stomata are developed 
either on both or only on one side of the leaf ; when the leaf is broad, as in Dammara 
and Salhburia, 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 Cycadeae and Coniferae 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 Cycadeae and of the broader leaves of Coniferae as 
the so-called Pallisade-tissue ; i. 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 Cycadeae 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 Abietinese the fibro-vascular bundle, 
split into two, is enveloped by a colourless tissue, which is 
sharply differentiated 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. Pinus Püiastey ; 
two cells of the colourless paren- 
chyma surrounding the fibro-vas- 
cular bundle of the leaf; t t the 
bordered-pits cut across, t' the 
same seen from the surface. 
carpus, Dacrydhitn, Torreya, Tsuga, Ctinninghmnia. 3. No canals in the root ; canals in the cortical 
parenchyma and in the pith of the stem : Salisbziria. 4. A secretory canal in the root ; canals in the 
cortical parenchyma of the stem: Cedrus, Abies, Pseudolorix. 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, Pseudotsuga. 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 Cycadese 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 Coniferae.] 
^ For further details see Mohl, Bot. Zeit. 187 1, Nos. i, 2. 
