35° 



PART IV. VEGETABLE TAXONOMY. 



Figs. 558 and 559 show, respectively, male and female prothallia 

 of this plant. 



The forms of Equisetinea?, at present in existence, are all 

 included under the one genus Equisetum, and this does not 



Fig. 558. 



Fig. 559. 



Fig. 558. — Male prothallium of Equisetum arvense; r, rhizoid; a, a, a, antheridia in 

 various stages of development. Magnified about 300 diameters. 



Fig. 559. — Part of female prothallium of Equisetum arvense. a, a, archegonia; b, 

 branch of prothallium; r, one of the rhizoids. Magnification about 300 diameters. 



contain a large number of species ; the individuals, however, 

 are abundant and widely distributed. Some of the species are 

 remarkable for the large amount of silica contained in the 

 epidermis. 



