CONIFERALES 



261 



A more bizarre stomatal region than that of Sciadopitys could not 

 be found in the entire order. The stomata are confined to a broad 

 groove on the abaxial face of the leaf (fig. 26gB). The epidermal 

 cells of this region have long, heavily cutinized projections, which 

 become shorter and shorter beyond the region of stomata, until, at 

 a few cells beyond the last stoma, there is 

 no projection and no more cutinization 

 than on the rest of the surface. 



The small, rigid leaves of Cryptomeria 

 have a single bundle and a single resin 

 canal (fig. 270). The walls of the epi- 

 dermal and hypodermal cells are very 

 thick, while the walls of the mesophyll 

 cells are thin, with none of the crenate 

 lobing so characteristic of the pines. 



Large, broad leaves like those of most 

 of the Araucariaceae and of many species 

 of Podocarpus, often look like the leaves 

 of dicotyls, and they often have a strong 

 palisade at the adaxial surface, with a 

 looser tissue below (fig. 271). The veins, 

 however, while appearing to be more or 

 less "parallel," are likely to show the 

 dichotomy so characteristic of the "par- 

 allel" veins of the cycads. 



The epidermis, and especially the sto- 

 mata, have recently been investigated 

 in great detail by Florin,'^^ who has 

 made a critical comparison of these fea- 

 tures in living and in fossil forms. This study not only adds to the 

 value of the epidermis and stomata as criteria in the phylogeny of 

 fossil plants, but indicates that these structures might well be 

 utilized in determining relationships of living forms. 



In the gymnosperms of the Carboniferous, in both the Cycado- 

 phyte and Coniferophyte lines, the double-leaf trace was a familiar 

 feature. In the hving Abietaceae the trace is double, but in the 

 Cupressaceae it is single. Some botanists doubt whether the double- 



FiG. 265. — Juvenile leaves: 

 Pinus laricio, early simple 

 leaves and later spur shoots, 

 each bearing a pair of needle 

 leaves. — From Chamberlain, 

 Elementary Plant Science (Mc- 

 Graw-Hill Book Co.). "5 



