EMBRYO AND SEEDLING OF DIOON SPINULOSUM 



Sister Helen Angela Dorety 

 (with plates X, Xl) 



Dioon spinulosum Dyer, imperfectly and incompletely described 

 by EiCHLER' in 1883, and by Dyer^* in 1885, but fully and carefully 

 by Chamberlain^ in 1909, is, like the other 2 species of Dioon, 

 endemic in Mexico. The embryos and seedlings which furnish 

 the material for this study were grown from o\'ules collected by 

 Dr. Chamberlain in the mountains about Tierra Blanca and Tux- 

 tepec during his several trips to the Dioon country. The tree is 

 described by him as a magnificent ornamental cycad 30-40 ft. 

 high. Unlike D. edule, it grows rapidly, and in 2 years makes a 

 handsome greenhouse plant with a crown of large, fernlike leaves. 



The unique appearance of the plant and the great size of its 

 ovulate strobilus and ovules led to the expectation of great pecu- 

 liarities in its vascular anatomy and cotyledonary arrangements. 

 The investigation has verified these expectations only in part. 

 The study of the vascular anatomy of the embryo and seedling of 

 D. spinulosum merely serves to emphasize the general harmony 

 which prevails among the cycads in this respect. 



Embryo 



The seed, like those of all cycads, is filled with a massive endo- 

 sperm stored with starch. Upon this tissue the proembryo and 

 embryo proper are nourished, apparently without any resting 

 period. When the embryo has attained a length equal to that of 

 the seed itself, pressure is exerted upon the stony coat, and the thin 

 region near the micropyle is broken. Fig. i shows a seed with a 

 young embryo borne on the twisted suspensor; fig. 2 represents 



' EiCHLER, a. W., Ein neues Z?/o(?«. Gartenflora 2:411. 1883. 

 " Dyer, Sir W. T. Thistletox, Biologia Central! Americana, Botany 3 : 190. 

 1885. 



3 Chamberlain, C. J., Dioon spimdosum. Box. Gaz. 48:401-413. 1909. 



251] , [Botanical Gazette, voL 67 



