68 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 

 Vegetative. 



Embryo and Seedling of Dioon spinulosum. — H. A. Dorety {Bot. 

 Gaz., 1919, 67, 251-6, 2 pis.). The material for this study was grown 

 from ovules brought by Dr. Chamberlain from Mexico, where the plant 

 forms a magnificent ornamental tree 30 to 40 feet high. The study of 

 the vascular anatomy of embryo and seedling emphasizes the general 

 harmony which prevails among the Cycads in this respect. The coty- 

 ledons vary in number from two to four, and are often lobed or divided ; 



Diagram illustrating girdling of leaf-traces in stem. 



in rare cases the cotyledonary sheath is undivided except near the tip. 

 They are mnltifascicular, resembling those of Ceratozamia and Micro- 

 ci/cas, rather than those of Zamia and Cycas, which have but few strands. 

 The arrangement and orientation of the vascular strands of cotyledons, 

 hypocotyl, stem, leaves and root, do not differ in any marked degree 

 from the general Cycad arrangement. The stem is large enough to 

 demonstrate the cause of the girdling habit ; each node of the stem is, 

 like the nodes on a first-year stem of foxglove, telescoped within the 

 older one instead of growing above it. The internodes are not elon- 

 gated because the primary meristcm of the stem- tip is held in check by 



