316 BOTANICAL GAZETTE [aprh 



protophloem and protoxylem are usually differentiated about th 

 same time, but the protophloem occasionally precedes the protoxylem. 

 The complete differentiation of the phloem is usually complete before 

 that of the xylem. The differentiation of the xylem in the too\> \- 

 much slower than in the leaf traces. Fig. 7 illustrates the structur 

 of a root bundle before it is completely developed and while it is still 

 in the cortex. The eccentric position of the bundle in mature root> i 

 shown in fig. 8. While the root bundle is making its way through 

 the cortex the endodermis is poorly differentiated, but in the matur 

 root outside of the stem it is well defined. The pericycle is poorly 

 developed. It is usually entirely absent opposite the phloem, but 

 opposite the xylem there is usually a small amount. 



THE LEAF 



echinosp 



(fig 



The leaves of the four species studied present considerable varia- 

 tion, both in general appearance and anatomy. 



'"•--■-''*• • • • r> puna is moderately stout, and 



- t _ & ™ w y/ . In the cortex and lower part of the 



leaf the bundle is fairly well developed, but above the sporangium it 

 becomes a slender strand. The bundle is collateral throughout, but 

 tends to become concentric in the upper part. The differentia i 

 of the phloem regularly precedes that of the xylem, as was foun ^} 

 Kruch (17) in the species which he studied. The protoxylem in mo 

 cases is plainly exarch, but sometimes the differentiation is nea^ 

 simultaneous. In this species I found no cases of distinctly mesa 

 protoxylem. It is common for the metaxylem to develop m 



three 

 hich it 



■ W% % £ I 



directions from the protoxylem, but I found no cases in * 

 developed on the fourth side, i. e., on the side toward the pw w 

 although Kruch and Scott and Hill find that in their s ^\ m 

 bundle tends to become mesarch in the region of the sP ™"? 



There is evidently a certain difference in this respect in ^ 



species, for in /. Nuttall 



sometimes Dresent. While 



or 



xylem are both composed of spiral and annular ~* ^ 

 tracheids with irregular spirals, the protoxylem can w • The 

 recognized by the fact that the spirals and rings are 00^ ^ ^ 

 protoxylem cells of the lower part of the leaf are small an 



