446 



MOSSES AND FERNS 



CHAP. 



occasionally is the first product of germination. As a not 

 infrequent occurrence may be mentioned also the suppression of 

 the first rhizoid (Fig. 258, C). The development for some 

 time is so varied that it is impossible to give any rule for it, but 

 generally the prothallium at this stage, like that of the lepto- 

 sporangiate Ferns, consists of but one layer of cells, and does 

 not show a midrib. These prothallia also do not have a definite 

 apical growth, and are usually more or less branched. Often, 



A. 



FIG. .159. A, Female prothallium with the first archegonium (ar), X7; B, male pro- 

 thallium, X7o. 



however, the prothallium while still small has a somewhat cy- 

 lindrical body composed of several layers of cells, and in these 

 the rhizoids are mainly confined to the base. The chloroplasts 

 which these at first contain are gradually changed into leuco 

 plasts, and may be completely absorbed (Buchtien (i), p. 17). 

 A comparison of the gametophyte with that of Lycopodiutn 

 cernuutn has been made (Jeffrey (2) , p. 186) , but as Goebel has 

 pointed out ((22), p. 409) there is this radical difference, in 

 Equisetum the prothallium is dorsi-ventral, as it is in the Ferns, 

 while in Lycopodiutn it is radially constructed. The more or 

 less evidently upright form assumed by the prothallium in 

 Equisetum is due to the amount of light. Normally the pro- 

 thallium of E. tclmateia is not upright, but more or less decid- 

 edly prostrate, as it is in the Ferns. (See Fig. 259, A.) 



