the other, and thus none of the prothalli of both ripen for fertiliza- 

 tion at the same time, but I think this would rarely happen. I have 

 found with every species I have raised from spores, that while many 

 of the prothalli develop plants at the same time, usually on the 

 same day, others remain apparently latent for long periods, some- 

 times for months. 



A third method, successfully used by Professor Bower in cross- 

 ing Polvpodiuui anreum and a variety of Polypodium vulgare, is 

 that of sowing the spores of each species separately, afterward 

 planting a prothallus of one species in close contact with a prothal- 

 lus of the other. This method offers more certainty of success, but 

 allows each species to retain both kinds of organs, which gives ex- 

 cellent opportunity for self-fertilization as well as for cross-fertiliza- 

 tion. 



A fourth method, pursued by Mr. Lowe, is that of sowing the 

 spores separately, afterward cutting the resultant prothalli into quar- 

 ters and planting a quarter of a prothallus of one species overlap- 

 ping a quarter of a prothallus of the other. In order that this 

 method may succeed, it is of course necessary that one of these 

 quarters shall contain archegonia and the other antheridia. Cutting 

 the prothalli in this way would probably as a rule isolate each kind 

 of organ. The danger of this method lies in the fact that the pro- 

 thallus is so small that by the slightest slip of the knife one might 

 accidentally leave a bit of tissue containing archegonia on an anther- 

 idial section, or vice versa. 



A fifth method, suggested by Mr. Davenport, and, so far as I 

 know, not tried by anyone heretofore, is that of sowing the spores 

 separately, cutting the resultant prothalli in two between arche- 

 gonia and antheridia, then planting an archegonial section of one 

 species in contact with an antheridial section of the other, so that 

 archegonia and antheridia coalesce. This is the methodl have used, 

 with the slight modification of cutting the prothallus into three sec- 

 tions instead of two ; cutting once transversely close to the sinus 

 and through the cushion of tissue on which the archegonia in most 

 species are borne ; cutting again transversely near the base, through 

 the root-hairs among which the antheridia are scattered, then dis- 

 carding the middle section and planting the upper (archegonial) 

 section of one species upright against the lower (antheridial) sec- 

 tion of the other, with the lower surfaces of both sections pressed 

 close together. Cutting in this way prevents, I think, all danger of 

 leaving both kinds of organs on the same section. There is some 



