344 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



was found to be a common feature, but sometimes as many as four 

 were distinguishable. 



Following Jeffrey's discovery, which has been confirmed by 

 Guerin (1930) for another species of Erythronium, a similar pro- 

 liferation of the embryonic cells was reported in Tulipa gesneriana 

 (Ernst, 1901) and Limnocharis emarginata (Hall, 1902). In the 

 latter the first division of the zygote is transverse and results in the 

 formation of a large basal cell and a small terminal cell. As a rule, 

 the former increases in size without undergoing any further divi- 

 sions. In some cases, however, it ''divides and subdivides to form 

 an embryogenic mass" from which several embryos bud forth as 



ABC 



Fig. 191. Cleavage polyembryony in Erythronium arnericanum. A, Upper part 

 of embryo sac, showing the "embryogenic mass" formed from zygote. B,C, 

 proliferation of embryogenic mass to give rise to embryos. (After Jeffrey, 1895.) 



in Erythronium. No older stages were seen, however, and it could 

 not be ascertained whether these embryos grow to full maturity. 



Most other cases of cleavage polyembryony reported since then 

 have been in the nature of abnormalities. Cook (1902) noted an 

 embryo sac of Nymphaea advena showing twin embryos which he 

 considered to have originated by the "splitting of a very young 

 embryo." Later, the same author (1924) observed one instance of 

 two embryos, and another of four, at the micropylar end of the 

 embryo sac of Crotalaria sagittalis. Since the synergids are quite 

 ephemeral in this plant, these embryos are believed to have arisen 

 by a splitting of the single zygotic embryo. Samuelsson (1913) 

 also reported a similar splitting of the proembryo in Empetrum 

 nigrum, Guignard (1922) in Vincetoxicum nigrum, and Johansen 

 (1931) in Zauschneria latifolia. In Lobelia syphilitica (Crete, 1938) 

 frequently one and sometimes two additional embryos develop at the 



