SPERMATOPHYTES: GYiMNOSPERMS 



191 



enhair tree (Gingko), with broad dichotomously veined 

 leaves, also develops mtilticiliate sperms. 



The testa of the seed, instead of being entirely hard as 

 described for pine and its allies, develops in two layers, the 

 inner hard and bony, and the outer pulpy, making the ripe 

 fruit resemble a plum. 



106. Conifers. This is the great modern Gymnosperm 

 group, and is characteristic of the temperate regions, where 

 it forms great forests. Some of the forms are widely dis- 

 tributed, as the great genus of pines (Pinus) (Fig. 158), 

 while some are now very much restricted, although for- 

 merly very widely distributed, as the gigantic redwoods 

 (Sequoia) of the Pacific slope (Fig. 159). The habit of 

 the body is quite charac- 

 teristic, a central shaft " "^ ** 

 extending continuously to 

 the very top, while the 

 lateral branches spread 

 horizontally, with dimin- 

 ishing length to the top, 

 forming a conical outline 

 (Figs. 160, 162). This 

 habit of firs, pines, etc., 

 gives them an appearance 

 very distinct from that of 

 other trees. 



Another peculiar fea- 

 ture is furnished by the 

 characteristic "needle- 

 leaves," which seem to be 



poorly adapted for foliage. These leaves have small spread 

 of surface and very heavy protecting walls, and show 

 adaptation for enduring hard conditions (Fig. 161). As 

 they have no regular period of falling, the trees are always 

 clothed with them, and have been called " evergreens." 

 There are some notable exceptions to this, however, as in 



FIG. 161. Cross-section of a needle-leaf of 

 pine, showing epidermis (e) in which 

 there are sunken stomata (ftp), heavy- 

 walled hypodermal tissue (es) which 

 gives rigidity, the mesophyll region (p) 

 in which a few resin-ducts (h) are seen, 

 and the central region (stele) in which 

 two vascular bundles are developed. 

 After SACHS. 



