HORSETAILS 91 



difference because when these spores germinate some develop 

 into male gametophytes, others into female gametophytes. 

 It appears to be a fact that if the spores are sown too thickly 

 only male gametophytes will be formed, but if thinly sown 

 female gametophytes will develop. If this is true then poorly 

 nourished spores develop into male gametophytes while fully 

 nourished spores develop into female gametophytes. The 

 development of the gametophytes of Equisetum and all the 

 other forms studied, can be readily observed by planting in 

 chemical solutions, because from these solutions specimens 

 can be taken daily and the development from the one-celled 

 spore stage to the filamentous stage and finally to the thalloid 

 prothallic stage with its innumerable cells and several 

 branches, can be readily observed. 



Male Gametophyte. The male gametophyte of Equisetum 

 arvense is smaller and less branched than the female game- 

 tophyte. Certain of the branches only produce antheridia; 

 some entire gametophytes produce only one antheridium. 

 An antheridium is spherical and has a wall composed of one 

 layer of cells. Sperms completely fill the space within the 

 wall. When these are mature the antheridial wall opens and 

 the multiciliated sperms swim out in the presence of moisture. 



Female Gametophyte. The female gametophyte produces 

 several archegonia. Each archegonium consists of neck, 

 composed of one layer of cells and several ventral canal cells, 

 and a venter or enlarged part which is imbedded in the tis- 

 sues of the female gametophyte. The venter contains the 

 egg cell. 



Fertilization. Fertilization is accomplished when the multi- 

 ciliated sperm enters the neck of the archegonium and its 

 nucleus fuses with the nucleus of the egg cell to form the 

 beginning of the sporophyte or asexual generation. The 

 young sporophyte is parasitic for a time on the gametophyte, 



