126 BOOKS AND CURRENT LITERATURE 



their behavior, the thickness of the leaf, the amount of photosynthate 

 already formed, the amount already stored in other portions of the 

 plant body, whether the leaf tissue is chiefly palisade or chiefly spongy 

 parenchyma, etc. appear from this study to exert considerable influence. 

 — H. E. Pulling. 



Morphology of the Cycads. — In a recent paper published in the 

 Botanical Gazette, 1 Sister Helen Angela Dorety, one of Chamberlain's 

 pupils, continues her morphological study of the cycads. The paper 

 deals with Dioon spinulosum, a Mexican form unique because of the 

 large size of the ovulate strobilus and ovules. The cotyledons which 

 vary in number from 2 to 4, resemble those of Ceratozamia and Micro- 

 cycas in the number of vascular strands. At a point where the cotyle- 

 donary strands leave the protostele of the hypocotyl, they are endarch, 

 becoming mesarch in the base of the cotyledon, and exarch near the 

 tip. Girdling is similar to that of other cycads and is very clearly 

 traced in diagrams in the paper. No extrafascicular cambium indicat- 

 ing relation to the polystele of the Cycadofilicales, is present. The 

 primary root is tetrarch changing to diarch as it develops. The paper 

 is clear and concise, and is illustrated with two plates of 28 drawings. — 

 J. G. Brown. 



1 Dorety, Sister Helen Angela. Embryo and Seedling of Dioon Spinulosum. 

 Bot. Gaz. 67! 251-256. 1919. 



