19 1 7] CHA MBERLAIN—L YCOPODIUM 63 



) 



The differentiation of the vascular tissues is interesting. A 

 short distance below the meristem the large cells which are to form 

 the largest tracheids are easily recognized, and some of the 

 cells of the points of the radial structure can be distinguished, 

 although lignification has not yet begun. Very soon the points 

 of the radial structure begin to lignify and are then marked off 

 very sharply from the surrounding tissues (fig. 17). These patches 

 of lignified tissue consist almost exclusively of coarsely pitted 

 tracheids. It is possible that there are some spiral vessels, but it 

 looks as if practically all of the spirally marked cells belong to the 

 leaf traces. If protoxylem is to be identified by spiral and annular 

 markings, very little of the tissue which becomes lignified at this 

 early stage would satisfy such a criterion; but the tissue is so 

 well defined and becomes lignified so far in advance of the rest of 

 the xylem, and is so sharply marked off from the large cells which 

 in longitudinal view have the typical scalariform marking, that it 

 may very properly be called the protoxylem. It should be recalled 

 that in the cycads spiral vessels in the protoxylem are largely 

 'confined to the seedling, the protoxylem of the adult plant consisting 

 almost exclusively of tracheids. 



The study of the root was not satisfactory. Near the tip the 

 bundle is C-shaped and diarch with the phloem in the sinus. 



The sporeling of L. volubile is comparatively slender and in 

 every way more delicate than that of L. scar io sum. In the upper 

 leafy portion the stele is quite regularly radial and tetrarch; but 

 from the secondary root (r in fig. 9) down to the pro thallium the 

 structure is regularly or irregularly triarch. In connection with the 

 more uniform topography of this stele, it should be noted that the 

 leaves and their single vascular strand are not nearly so robust 

 as in L. scariosum. The adult stele has the banded arrangement. 

 The differentiation of the tissues of the stele proceeds as described 



for L. 



scariosum. 



Summary 



1. Lyco podium laterals has a green, leafy prothallium, and there 

 is a protocorm-protophyll stage in the embryogeny. L. volubile 

 and L. scariosum have subterranean prothailia with no protocorm 

 stage, but the early leaves have the structure of protophylls. 



