XII 



EQUISETINEM 



The Sexual Organs 



447 



The prothallia of Equisetum are usually dioecious and, as is 

 usual in such cases, the males are smaller and the antheridia 

 develop first. The latter generally appear in about a month. 

 In E. telmateia there is not so much difference in the appear- 

 ance and size of the male and female plants, and they are not 

 always distinguishable by the naked eye. 



The first antheridia in E. pratense (Buchtien (i), p. 21), 

 may appear within four weeks on vigorous prothallia, and are 

 found at the tip, or upon the forward margin of the prothallium. 

 After the first marginal antheridia are formed, there is inau- 

 gurated an active division in the cells immediately adjacent, and 

 a sort of meristem is developed from which new antheridia 



Fig. 260. — Development of the antheridium, X 190. A, Longitudinal section through 

 the antheridial meristem showing antheridia of different ages; B, longitudinal sec- 

 tion of young antheridiura, X375: C, two sections of a terminal, single antheridium, 

 nearly ripe, X190; D, three transverse sections of young antheridium, X190; 

 o, opercular cell. 



arise, much as is the case in E. telmateia. While in the latter 

 species, as in others, the antheridia may arise at the ends of 

 the prothallial branches, they also may be formed upon a meris- 

 tem quite like the archegonia, and are usually in groups, so that 

 longitudinal sections show antheridia of very different ages, all 

 evidently derived from the activity of the meristem (Fig. 260, 

 A). The development shows a close resemblance to that of 

 the eusporangiate Ferns, and in connection with the other points 

 in the growth of the gametophyte and sexual organs, suggests 



