PTERIDOPHYTA 



293 



the sporophyte is most characteristic, the hollow, jointed shoots and 

 rudimentary leaves presenting a marked contrast to the Ferns. The 

 sporophylls are always arranged in a cone at the apex of the shoot, 

 and the globular green spores, which germinate at once, are pro- 

 vided with hygroscopic appendages, or elaters. 



The Gametophyte 



The germination of the spores begins within a few hours, and within twenty- 

 four hours the root-hair is cut off from the larger prothallial cell. The latter shows 

 more or less irregularity in its development, and the gametophyte shows more 

 variation in its growth than is usually the case in the Ferns. Sometimes, but not 

 always, a definite apical cell can be found in the young gametophyte. The older 



FIG. 259. Equisetum telmateia. Antheridium. A, section of antheridial meristem, 

 with three antheridia of different ages (X 190). , young antheridium (x 375). 

 (7, two longitudinal sections of a nearly ripe antheridium (x 190). Z>, three 

 transverse sections of young antheridium (X 190) ; o, opercular cell. 



gametophyte (Fig. 258) is an irregularly branched, green plant, not unlike the 

 gametophyte of some of the lower Ferns, or the thallus of some Liverworts. 

 When fully grown, it generally shows an axial, fleshy body, with numerous 

 irregular leaflike lateral lobes. There is an apical meristem, which gives rise to 

 several short dichotomous shoots. The prothallia are usually dioecious, the male 

 plants being generally smaller and more irregular in shape than the female. 

 The sex of the prothallium is largely a matter of nutrition, the better nourished 

 ones being usually female, the others male. It Las been demonstrated that a 

 prothallium which has already developed archegonia can, by insufficient feeding, 

 be forced to develop antheridia. 



Antheridium. The antheridia are first formed within a month or six weeks 

 after the spores are sown. They develop either upon the lateral branches or 

 they may (in E. telmateia) be formed upon an apical meristem in much the same 

 way as the archegonia are. In their development they correspond very closely 

 to those of the Marattiacese, and, like the latter, there may be present a trian- 

 gular opercular cell. In the development of the large, multiciliate spermato- 



