GNETALES— GNETUM 425 



described sperm nuclei of equal size, and believed that both were 

 functional, since fertilized eggs were usually found in pairs. Lotsy 

 believed that the number of pollen tubes which had entered an egg 

 could be determined by counting the number of pairs of zygotes. 



Thompson's figure (395 Z)) is described as a two-celled proembryo. 

 It looks much hke a pair of zygotes, as described by Lotsy. If it is a 

 two-celled embryo, as seems Hkely, there is no free nuclear stage in 

 the embryogeny, and Gnetum, like Sequoia, has reached the angio- 

 sperm level in another feature of its development. 



Whether the figure represents a two-celled proembryo or a pair 

 of zygotes, the next stage is the development of a tube, the suspen- 

 sor, from each of the two cells (fig. 395 E). The nucleus divides, and, 

 of the resulting nuclei, the one in advance undergoes free nuclear 

 division, producing four nuclei, from which the embryo is organized 

 (fig. 395 7*", G). The other nucleus does not divide. 



It is very desirable that fertilization and embryogeny be worked 

 out in cytological detail, not only in Gnetum, but in the other two 

 genera. Investigators familiar with other gymnosperms may have 

 wondered why Lotsy, Pearson, and Thompson, with material at 

 hand, left some features undecided; but the reason is evident when 

 one attempts to make preparations, especially of the male gameto- 

 phytes of Welwitschia and Gnetum. However, the problems can be 

 solved if fresh material is fixed in very small pieces, for these two 

 genera are no more difiEicult than Ephedra, in which Land gave a 

 very com.plete account of spermatogenesis. 



The intermediate and later stages in the embryogeny are still to 

 be described. 



CAYTONIALES 



At this time no account of the gymnosperms would be quite com- 

 plete without some mention of the Caytoniales inasmuch as they 

 possess some gymnosperm features and are so regarded by some 

 botanists. Thomas'^'^ account, which refers to the order as angio- 

 sperms, was based upon megasporophylls, fruits, and seeds of Gris- 

 thorpia nathorsti and Caytonia sewardi; microsporophylls or stamens, 

 Antholithus arheri; and fragments of associated leaves, Sagenopteris 

 phillipsi. These investigations revealed a closed carpel with stigma 



