THE HIGHER CRYPTOGAMIA. 297 



for them, I have never found the prothallia of any species in 

 their natural state. Even under culture, the greater number 

 of the prothallia decay before the development of antheridia, 

 or are destroyed by insects, or by an overgrowth of 

 Vaucheriae, Oscillatoriea?, or proembryos of mosses. Before 

 1852 very few of the prothallia of Equisetum arvense which 

 I had cultivated lived beyond the fifth month after the 

 sowing. They were all of the male sex. In some I ob- 

 served the formation of a short, flat, lateral shoot, which 

 produced the rudiments of archegonia. This was the only 

 instance of departure from the disecious character which 

 ever occurred to me in the prothallia of Equiseta. 



Those prothallia of Eq. arvense, variegatum, and palustre, 

 which produce archegonia never produce antheridia,* 

 They ramify to a much greater extent and become far more 

 vigorous than the male prothallia. A female prothallium 

 is normally a circular combination of from three to six 

 fleshy masses of cellular tissue, which bear very numerous 

 green crisp shoots of more delicate texture, and from a 

 quarter to half an inch in diameter. The form very much 

 resembles that of young plants of Antkoceros punctatus. 



When male and female prothallia are produced from 

 spores sown contemporaneously, the archegonia of the 

 female prothallia appear much later than the antheridia of the 

 male ones ; the younger female prothallium would seem to be 

 sterile. The spores from which female and male prothallia 

 originate are exactly of the same size and quality. Exter- 

 nal circumstances seem to have an influence upon the 

 germinating prothallia. A dry place exposed to light 

 seems decidedly to favour the development of male pro- 

 thallia of Equisetum arvense. The spores of Equisetum 

 arvense and pratense when sown artificially produced prin- 

 cipally male prothallia, t and those of Equisetum palustre 



* On the other baud Bischoff lias found the prothallium of Eq. sylvatium 

 beariug archegonia on its older portions and antheridia on its younger shoots. 

 ( [ Bot. Zeit.,' 1853). 



f In 1S49, 50, and 51, I obtained only male prothallia, upon which rudi- 

 ments of archegonia appeared only at a late period, and then only upon adven- 

 titious shoots. In the summer of 1852 the number of male prothallia was 

 greater by about one half than that of the female ones. That summer seems to 

 have been especially favorable to the germination of Equisetum. Cultivated 

 specimens of Equisetum variegatum shed spores at the beginning of May. 

 About the middle of July female prothallia, which were present in great 

 numbers, developed small leafy plants. 



