CYCADALES 107 



branch, so that the cotyledons contain only four vascular strands, and 

 this seems to be true also of some species of Cycas, of Macrozamia, 

 and of Stangeria; but in Ceratozamia the branching may reach twelve 

 cotyledonary strands; and in Dioon spinulosum, Microcycas, and 

 Bowenia the branching is even more extensive. When the root is 

 diarch, as in some species of Cycas, it is the intercotyledonary poles 

 that are suppressed, and although the corresponding strands are 

 represented in each cotyledon, their basal endings are free in the cor- 

 tex. The leaf traces are usually four in number; the two inner ones 

 arising from the proximal side of the central cylinder and being more 

 or less direct; the two outer ones arising from the distal side of the 

 central cylinder and forming the characteristic girdles of the cortex 

 in their course to the leaf. 



In a general review of seedling anatomy Miss Thomas (57) con- 

 cludes that in all cycads four or six vascular strands enter the cotyle- 

 don, and that the primary root is prevailingly tetrarch, with a strong 

 tendency to become reduced toward the apex to the triarch or diarch 

 condition. For example, in Cycas siamensis there are four cotyle- 

 donary strands, but in connecting with the root two of the strands 

 (the intercotyledonary ones) die out and the root is diarch. 



In a similar review of the seedling anatomy Hill and De Fraine 

 (67) conclude that the number of vascular bundles at the base of each 

 cotyledon ranges from two to eight; that these bundles in general 

 are mesarch and become exarch; that the transition phenomena 

 occur so rapidly that most of the hypocotyl shows root structure; 

 that the cotyledonary strands are not of equal value in the production 

 of root structure; and that after the initial root structure is attained 

 the number of poles may be increased at lower levels. 



Certain occasional situations have been recorded, which are inter- 

 esting not only in what they imply, but also in suggesting a search 

 for their wider occurrence. For example, the concentric bundles 

 at the base of the cotyledons in Stangeria, the polystelic condition in 

 the earlier stages of the peduncle of Encephalartos, the cortical strands 

 in the base of the peduncle of Dioon (61), and the mucilage canals 

 in the root of Dioon are all features that fit into the general anatomi- 

 cal condition of the cycads, as described above. 



In his conclusions from an investigation of the vascular anatomy 



