118 MOKPIIOLOGY OP SPERM ATOPHYTES 



with bordered pits are entirely lacking, simple pitted and spiral 

 vessels replacing them. In connection with the vascular bun- 

 dles there is a conspicuous development of fibrous sclerenchyma. 

 In the stem as a whole parenchymatous tissue largely predomi- 

 nates, and forms a conspicuous water-reservoir system. 



Perhaps the most remarkable anatomical feature is the occur- 

 rence of the so-called " spicular " cells, found in large numbers 

 and scattered throughout all organs. They are very large, fusi- 

 form or branched, straight or variously curved, with greatly 

 thickened walls, in the outer layers of which many finely formed 

 crystals of calcium oxalate are imbedded close together. 



Gnetum. — As in Tumboa, the primary cambium is short- 

 lived, and successive cortical cambium zones organize concentric 

 series of cauline bundles. As in Ephedra, the xylem contains 

 vessels of the true tracheary type associated with tracheids of the 

 Gymnosperm type. 



THE LEAF 



Ephedra. — The opposite leaves of Ephedra are reduced to 

 scales, which coalesce to form at each node a two-toothed sheath. 

 The occurrence of true foliage leaves seems to be extremely rare. 



Tumboa. — In the single pair of long-lived parallel-veined 

 leaves the stomata are in rows and deeply sunken. The chloro- 

 phyll-bearing tissue beneath the epidermis ensheaths a promi- 

 nent central tissue which is colorless or nearly so, and consti- 

 tutes a conspicuous waiter reservoir. The colorless middle tis- 

 sue is traversed by the very numerous and strong parallel 

 bundles, which are connected by transverse branches. These 

 branches sometimes end freely in the mesophyll, or send out 

 branchlets which end blindly. While the general system of vena- 

 tion is of the monocotyledonous type, the blind ending of certain 

 branches is a dicotyledonous feature. 



Gnetum. — The leaves of Gnetum seem to differ in no essen- 

 tial feature from such leaves of Dicotyledons as are leathery in 

 texture, having a typical reticvilate bundle system of the pinnate 

 variety. 



THE EOOT 



The very meager accounts of the roots of Gnetales have refer- 

 ence only to species of Ephedra. From these it appears that 

 the group possesses the same peculiarities shown by the other 



