GYMNOSPERMAE. 



345 



in which many finely-formed crystals are imbedded close to one another. Similar 

 forms are also found in the Coniferae. 



The parenchymatous fundamental tissue of the Coniferae is very much diminished 

 in quantity as the age of the stem and root increases ; besides the slender pith the 

 stem is now exclusively composed of the products of the cambium-ring, as the primary 

 cortex, and then the outer continually developing layers of the secondary cortex 

 are used to form bark. In the Cycadeae, which have but small growth in thickness, 

 there is very little formation of cork, and in Welwitschia there appears to be none 1 ; 

 but this is perhaps doubtful. 



Sap-conducting intercellular passages are widely distributed in the Gymnosperms, 

 and are lined with secreting epithelial cells. In the Cycadeae they traverse all the 

 organs in large numbers and contain gum, which exudes from transverse sections in 

 large viscid drops ; in the Coniferae they contain oil of turpentine and resin, and occur 

 in the pith of the stem, in the whole of the wood, in the primary and secondary cortex, 

 and in the leaves ; like the gum-passages of the Cycadeae they always follow the 

 longitudinal direction of the organs. In many Coniferae with short leaves roundish 

 resin-glands are also found in the leaves, as in Callitris, Thuja, and Ciepressies, accord- 

 ing to Thomas ; Taxus has no resin-passages at all 2 . 



The foliage leaves of the Cycadeae and Coniferae are usually covered with a stout 

 strongly cuticularised epidermis with numerous stomata, and each stoma has two 

 guard-cells. In the Cycadeae the stomata are found only on the 

 under surface of the leaf and more or less sunk in its tissue, and are 

 either scattered irregularly or placed in rows between the veins 

 (Kraus). In the Coniferae also, according to Hildebrandt 3 , the 

 guard-cells are always sunk in the epidermis of the leaves, and the 

 stoma therefore always has a vestibule. The stomata in the Coniferae 

 occur on both sides or only on one side of the leaf; if the leaf is 

 broad, as in Daminara and Gingko, they are scattered about without 

 any order, if the leaves are acicular they are usually arranged in 

 longitudinal rows ; they are arranged in rows even in the large leaves 

 of Wehuitschia. The firm texture of the leaves of the Cycadeae and 

 Coniferae is due to a hypodermal layer, often of considerable thick- 

 ness, consisting of cells which are usually long and fibre-like with 

 much-thickened walls and lying parallel to the surface of 'the leaf; in 

 the leaf of Welwitschia this hypodermal tissue is loose and succulent 

 and is traversed by fibre-bundles 4 , and it acquires firmness by means 

 of a mass of spicular cells. Beneath the hypodermal layers is the tissue 

 containing chlorophyll, which in the Cycadeae and in the Coniferae 

 with broader leaves is developed on the upper side of the leaf in the 

 form of palisade-tissue, that is, the cells are elongated in a direction perpendicular to 

 the surface of the leaf and are closely crowded together ; the cells containing chlorophyll 

 in the leaf in the genera Pinus, Larix; Cedrits have infoldings of their cell-wall. The 

 middle layer of the tissue of the leaf, in which the vascular bundles run, is developed 

 in a peculiar manner in most Gymnosperms ; in the Cycadeae and Podocarpeae it 

 consists of cells which are elongated in a direction transverse to the axis of the leaf 

 and to the bundles, but lie parallel to the surfaces of the leaf, and leave large inter- 

 cellular spaces (the transverse parenchyma of Thomas, the transfusion-tissue of Mohl) ; 

 in the acicular leaves of the Abietineae the divided vascular bundle has an investment 

 of colourless tissue which is clearly distinguished from the surrounding chlorophyll- 

 tissue ; it is parenchymatous and marked by a large number of peculiar pit-like 

 formations (Fig. 266) 5 . 



FIG. 266. Finns 

 pintzsfer. Two cells . 

 of the colourless pa- 

 renchyma surrounding 

 the vascular bundle of 

 the leaf; at/< the pit- 

 like formations seen in 

 section, at f the same 

 seen from the surface. 



1 Flora, 1863, p. 473. 

 3 Bot. Ztg. 1869, p. 149. 



- For further information see De Bary, Vgl. Anal., p. 137. 



* Flora, 1863, p. 490. 

 5 Mohl in Bot. Ztg. 1871, Nos. 1-2. Zimmerman in Flora, 1879. 



