138 



MOSSES AND FERNS 



CHAP. 



not show any definite apical growth. The plant at this stage 

 has a striking resemblance to the prothallium of Equisetum. 

 With the appearance of the marginal lobes, the first of the 

 mucilage slits appears upon the ventral surface (Fig. 6^^, and 

 from time to time surface cells grow out into the delicate 

 rhizoids, and a little later the first dichotomy of the growing 

 point takes place. Up to this time the young plants appeared 

 entirely free from Nostoc, but soon after they were found to 

 be infected, which no doubt was connected with the formation 

 of the mucilage slits through which the Nostoc enters the 

 thallus. 



Dendroceros includes about a dozen species of tropical Liver- 



FiG. 67.- — Anthoceros fiisiformis (Aust.). A, Young plant showing the first rhizoid (r) ; B, upper part 

 of an older one with the first mucilage cleft {st) ; x, the growing point, X215. 



worts, which are distinguished at once from Anthoceros by the 

 very characteristic form of the thallus. This has a massive 

 midrib, projecting below, but the rest of the thallus is but one 

 cell thick and forms lateral wings which are much folded 

 and lobed, so that the aspect of the plant is somewhat like a 

 Fossombronia. As in Anthoceros, some species have a perfectly 

 compact thallus without intercellular spaces {D. cichoraceus), 

 while in others these are very much developed and the thallus 

 has a more or less spongy texture, i.e. D. Javanicus. This 

 development of the thallus and sporogonium has been studied 

 only by Leitgeb,^ and in the main seems to correspond very 



" Leitgeb (7), vol. v. p. 39. 



