﻿2l6 RELATIONSHIPS. 



attached to a minute elevation, to which the dehiscent slits are radial; whence 

 alignment in sori is more apparent after the discharge of pollen. In development 

 the sori, moreover, agree with those of Angiopteris, the general structure of the 

 sporangia being likewise Marattiaceous (figs. 124 and 125). As bearing directly 

 on the existence of a fundamental relationship to the Cycadeoidete, it should be 

 recalled that for quite thirty years, resting mainly on the investigations of Eugen 

 Warming, the derivation of the staminate scales of the cycads from fertile fern 

 fronds of the Marattiaceous type has been one of the best defended and most widely 

 accepted of all working botanical hypotheses; and indeed, with the discovery of 

 the pollen-bearing synangia of the Cycadeoidea; so exactly similar in structure to 

 the spore-bearing synangia of Marattia in the first instance, and the later discovery 

 of such seed-bearing " quasi-ferns " as Lagenostoma in the second, this hypothesis, 

 to say the least, has taken on the guise of a demonstrated truth. 



The structure of the three-celled pollen is much as in Ginkgo. In germina- 

 tion a small persistent lenticular prothallial cell is cut off. Then a generative cell 

 is cut off in contact with the prothallial cell, the large cell left over being the 

 vegetative or " tube cell," and its nucleus the tube nucleus. In Ginkgo the same 

 alignment is present, except that there is clearly an initial resorbed cell, traces of 

 which have, however, also been observed in the cycads (69, 186). 



In fertilisation the generative cell plays an extraordinary role, but recently 

 brought to light by the brilliant researches of Hirase on Ginkgo (66, 67) in the 

 primary instance, and rapidly followed by those of Ikeno (69) on Cyras and of Web- 

 ber (186) on Zaniia. Immediately following the development of this three-celled 

 stage, the large vegetative cell of the pollen grain pushes in the wall of the gen- 

 erative cell and at the same time elongates to form the pollen tube, which then 

 invades and branches more or less freely in the nucellar tissue, also earning with it 

 the tube nucleus. Meanwhile the generative cell divides into a quiescent stalk and a 

 body cell with an immense nucleus, at whose opposite poles arise the radiately struc- 

 tured cilia formers or blepharoplasts of Webber. Then the tube nucleus makes 

 a retrograde movement from its position in the end of the branches, invading the 

 nucellar tissue and consorting with the basally situated stalk and body cell. Next the 

 nucleus of the latter divides in the equatorial plane and inaugurates the formation, 

 from the body cell contents, of the two spermatozoids, each of which bears a broken 

 ciliferous spiral organized from the adjacent polar body or blepharoplast. The 

 spermatozoids are of large size, visible to the unaided eye, and in effecting fecundation 

 after the rupture of the pollen tube swim actively to the archegonium, the watery 

 medium for this last stage of the journey of the ciliated sperm cells being afforded in 

 part by the tube contents and in part by exudation from the egg cell, rather than 

 from external moisture. The spermatozoids may, however, be observed swimming 

 free in sugar solutions, a highly suggestive fact, since there is absolutely no inferen- 

 tial doubt that such motile male cells took part in fertilization in the Cycadeoidese. 

 It is, moreover, highly probable that owing to the non-cleistogamous character of 

 the flowers of the latter, and the much inclosed ramentum-covered position of 

 the ovulate strobili that the antherozoids were capable of swimming considerable 

 distances through such water and moisture as was present during the season of 



