^;^2 PHANEROGAMS, 



pits and hence with a more or less scalariform wall are very much like the long prosen- 

 chymatous vessels of Vascular Cryptogams ; and this resemblance extends even to 

 the tracheidcs of Goniferae, so far as they are distinctly prosenchymatous, although the 

 smaller number and round form of the bordered pits shows a more marked difference. 

 The bordered pits of Coniferae are usually developed only on the wall which faces the 

 medullary rays, in one or two rows, but in Araucaria in larger numbers and densely 

 crowded. In the structure of the secondary wood, as in that of their flowers and 

 in their habit, Gnetaceae approach Dicotyledons; in Ephedra broad vessels occur in 

 it together with the usual tracheides in the inner part of the ring of wood, but their 

 component ceUs are separated by oblique septa, and are therefore still prosenchymatous, 

 and are penetrated by several roundish holes ; their lateral walls show bordered pits like 

 the tracheides, and furnish a striking evidence that the true vessels in the secondary 

 wood of Dicotyledons are connected by intermediate forms with the vessels of Vascular 

 Cryptogams formed from prosenchymatous cells. In the wood of Welwhschia tracheides 

 with doubly bordered pits are also present. 



The medullary rays of the secondary wood of Coniferae are very narrow, often only 

 one cell in breadth ; the cells are strongly lignified, and their lateral faces in contact with 

 the adjoining tracheides are provided with closed bordered pits. In Cycadeae the rays are 

 broader, and their tissue bears a closer resemblance to the parenchyma of the pith and 

 cortex ; their number and width cause the whole substance of the wood to appear spongy, 

 and its prosenchymatous cells are seen to be strongly curved in different directions in 

 tangential sections. The phloem-portion of the fibro-vascular bundles of Gymnosperms 

 resembles that of Dicotyledons ; it is mostly composed of true strongly-thickened bast- 

 fibres, cambiform cells, latticed cells, and parenchymatous cells ; while in Coniferae they 

 are formed in alternate layers. Usually the soft bast predominates. 



The Fundamental Tissue of the stem of Gymnosperms is separated by the ring of wood 

 into pith and primary cortex. Both are very strongly developed in Cycadeae, especially 

 the pith, and consist of true parenchyma, while the woody portion is considerably 

 smaller. In Wehvitschia the parenchymatous tissues appear also to predominate ; but 

 the greater part of their substance is the product of the activity of the meristem-layer of 

 the stem already mentioned. A large number of so-called spicular cells occur dispersed 

 in all the organs of this remarkable plant, they are fusiform or branched and greatly 

 thickened ; and a number of beautifully developed crystals are found imbedded close to 

 one another in their cell-wall. Similar structures also occur in Coniferae (p. 66). 



The parenchymatous fundamental tissue of Coniferae decreases greatly with the 

 increase in age of the stem (and of the root). With the exception of the pith, which is 

 here small, the stem consists exclusively of the products of the cambium-ring, since the 

 primary cortex, and afterwards also the outer layers of the secondary cortex which 

 always have a subsequent growth, are used up in the formation of cork. In the stem of 

 Cycadeae, the increase of which in thickness is inconsiderable, the formation of cork is 

 also very small; in fVelivitschia it appears to be entirely wanting (?). 



Intercellular Passages are widely distributed in Gymnosperms ; their structure is that 

 which has been explained generally at pp. 78 and 94. In Cycadeee they are found in all 

 the organs in large numbers, and contain gum, which exudes from incisions in thick 

 viscid drops ; in Coniferae they contain oil of turpentine and resin. In this latter order 

 they occur in the pith of the stem, in the whole substance of the wood, and in the 

 primary and secondary cortex, as well as distributed through the leaves ; always 

 following the direction in length of the organs, like the gum-passages of Cycadeae. 

 In many Conifers with short leaves roundish resin-glands also occur in them (as in 

 Callitris, Thuja, and Cupressus, according to Thomas) ; in Taxus the resin-canals are 

 entirely wanting ^. 



^ [Van Tieghem (Ann. des. Sci. Nat. 1872) distinguishes the six following modifications of the 

 distribution of the secretory organs in Coniferae: — r. No canals in the root nor stem: Taxus. 2. No 

 canals in the root ; canals in the cortical parenchyma of the stem : Cryptomeria, Taxodinm, Podo- 



