8 MORPHOLOGY OF SPERMATOPHYTES 



Cycas the pinnae are circinate, and in Zamia, C eratozamia, and 

 Stangeria the leaf axis is circinate. In general, two leaf traces 

 connect the vascular systems of the stem and leaf, sometimes 

 bending and passing almost horizontally through the cortex, 

 sometimes, as found by Worsdell 21 in Macrozamia, passing 

 tangentially close beneath the surface for some distance and 

 gradually turning inward to the stem system. Upon entering 

 the leaf the two bundles break up variously, and the vein system 

 is characterized by the comparatively small amount of anasto- 

 mosing and the frequency of dichotomy, as in Encephalartos. 



The anatomical structure of the leaves is quite similar to 

 that of the broad leaves of certain Conifers (Fig. 5). The 

 epidermis is strongly cuticularized, and the stomata occur only 

 on the lower surface, the guard cells being deeply sunken. The 

 leathery texture is due to a strong hypodermal development of 

 thick-walled, almost fibrous cells, beneath which is the display 

 of mesophyll. A distinct palisade region is organized, but the 

 colorless middle region, in which the veins run, is peculiar. It 

 consists of cells elongated transversely to the leaf axis and parallel 

 with the surface, and large intercellular spaces, and may repre- 

 sent the " transfusion tissue " of Yon Mohl. The absence of chlo- 

 rophyll and the elongation of the cells has suggested a conducting 

 region to compensate for lack of the branching and anastomosing 

 of veins. The same structure occurs among Conifers in Sciado- 

 pitys and other broad-leaved forms ; while in the needle leaves 

 the regular transfusion tissue, more definitely differentiated, is 

 within the bundle sheath. 



THE EOOT 



The primary root continues as a tap root, but numerous 

 branches and secondary roots extend in every direction, the 

 latter often extending upward and reaching the surface. An 

 interesting phenomenon connected with these upward rising 

 root branches, which often spread in feltlike masses about the 

 base of the stem in species of Cycas, Macrozamia, Ceratozamia, 

 Dioon, and other genera, is the occurrence upon them, usually 

 at the tip, of short " coral-like " branches, usually in clusters 

 (Fig. 6). These peculiar branches have been called " tuber- 

 cles," but they do not have the structure of the bodies which 

 receive that name in certain Leguminosae, being much modified 



