1914] 



HILL— A NA TOM Y OF LI COPODI UM 



65 



mass of cells and the portions of the cylinder just within the endo- 

 dermis are occupied by groups of smaller cells which have relatively 

 very large nuclei and dense cytoplasm. These smaller cells are the 

 parenchyma of the cylinder and will give rise to both the protoxylem 

 and the phloem elements (fig. 2). 



The cylinder of the vegetative apex is more nearly circular 

 in outline than that of the strobilus. The two show similar 

 differentiation and differ little 

 excepting that the cylinder 

 of the vegetative shoot has 

 about twice the diameter of 

 that of the strobilus, and the 

 extent of the group of large 

 cells is greater, with more 

 numerous groups of small 

 parenchyma cells. 



In the further organization 

 of the stele, the protoxylem is 

 the first to be differentiated. 

 The protoxylem points arise 

 in irregular succession in the 

 peripheral region of the cyl- 

 inder by the lignification of 

 some of the small cells. Gen- 

 erally there is only one cell 



lignified first, and usually this Fig. 3— L.carinatum: transverse section of 



cell is situated in the second the strobilus axis ' s , howing th , e , radial ammge " 



layer of cells from the endo- 



ment; px, protoxylem; p, phloem; X5o°- 



dermis 



This is followed by the lignificat 



of some of the 



smaller cells similarly 



at first one layer of cells in thickness. 



This leaves a pericycle, 



iere are 2- a nrotoxvlem 



points differentiated in the strobilus apex, and a large number, 

 generally 6 or 8, in the vegetative apex. These points are located 

 at the peripheral ends of the radiating strands of the central group 



unlignified 



This is the regular situation in the 



vegetative apex, but when there are only 2 protoxylem points 

 in the strobilus apex, the relation of the protoxylem and the 



