122 BOTANICAL GAZETTE [august 



gradually a horizontal position, and with subsequent growth are 

 lengthened and the expanse increased. ,; Matte (9) and Sister 

 Helen Angela (3), in connection with Ceratozamia, both describe 

 a similar vertical position of traces in the early developmental 

 stages, girdling becoming evident with the increase in diameter 

 of the inclosed group of leaves and stem. In more recent investi- 

 gations of Dioon edule by Thiessen, and of D. spinulosum by 

 Sister Helen Angela (4), however, both authors maintain that 

 the girdles are established very early, and that their horizontal 



course is laid down from the beginning. , 



The results of the present investigation indicate two possi- 

 bilities therefore. Either the arrangement of cortical strands in 

 the older seedlings and adult wood of Dioon spinulosum differs 

 from that found in the embryo and very young seedlings of both 

 species of Dioon, or the preceding statements need considerable 

 modification. 



At the very tips of the two-, three-, and ten- year-old seedlings 

 (fig. 10) the perpendicular arrangement of the lateral strands and 

 their connection with the horizontal girdles is unmistakable. 

 It is reasonable to suppose, therefore, that the arrangement of 

 foliar strands in the first leaves of the young seedling would be 

 substantially the same as that characterizing the leaves of the 

 older seedlings, save that (1) the very young strands having their 

 origin in the cotyledonary plate would ascend vertically for a 

 shorter distance before anastomosing to form the horizontal 

 girdles, and (2) there would be likely to be a decrease in the number 

 of strands leaving the vascular plate for each leaf base. 



Another question of importance is the significant relationship 

 suggested by the distribution of leaf traces in the seedlings of 

 D. spinulosum. Thus we find numerous strands (varying from 

 7 to 9) passing obliquely upward into each leaf base, each one of 

 which causes a gap of its own in the main stele. As previously 

 indicated, however, these strands do not all enter the petiole. 

 There is instead an anastomosis of traces in the sheathing base of 



the leaf, resulting in the conspicuous and characteristic horizontal 

 girdles, which correspond in many respects to the marginal vein of 





