37° 



MORPHOLOGY OF GYMNOSPERMS 



the mesophyll sheaths a conspicuous, central, nearly colorless tissue 

 which constitutes a water reservoir. This colorless middle tissue is 



traversed by the very numer- 

 ous and strong parallel 

 bundles, which are con- 

 nected by transverse 

 branches. These branches 

 sometimes end freely in the 

 mesophyll, or send out 

 branchlets that end blindly. 

 It follows that while the 

 parallel course of the prin- 

 cipal veins is monocoty- 

 ledonous, the blind ending 

 of some of the veinlets is 

 dicotyledonous. 



The leaves of Gnetum 

 seem to differ in no essen- 

 tial feature from those of 

 dicotyledons with leathery 

 texture, being pinnately and 

 reticulately veined, so that 

 the plant, except when in 

 fruit, might be mistaken 

 for a dicotyledon (fig. 



413)- 



This assemblage of 

 leaves is more puzzling than 

 suggestive, and if the genera 

 are really of common an- 

 cestry, it implies a, history 

 and a range of forms that remain to be discovered. 



Fig. 413. — Gnetum Gnemon: from a photo- 

 graph of a plant at the University of Chicago. 



2. The spore-producing members 



The strobili of Gnetales are compound, each strobilus being a 

 catkin-like cluster of simple axillary strobili, which resemble flowers, 

 especially since their bracts are arranged like a perianth. While 



