23 



ception, appeared. This exceptional plant may have been the result 

 of asexual growth. Mr. Lowe attributes it to an insect carrying an- 

 therozoids from a distance, but there is not time to discuss this pos- 

 sibility. If the sections do replace the missing organs, this fifth 

 method, as well as all the others except the first described, can be 

 used for testing the hybridity of a fern only in cases where the 

 alleged hybrid is so distinct from both of its supposed parents that 

 it could not possibly arise from the self-fertilization of either one. 



Of such a nature are Asplenium ebenoides and Aspidium cris- 

 tatum x marginale. I suppose no one will question for a moment 

 that Asplenium ebenoides cannot be considered a variety of either 

 Asplenium ebeneum or Camptosorus rhizophyllus, but must either 

 be a cross between the two or a distinct species. Now a distinct 

 species certainly could not arise from a prothallus of another species, 

 either from self-fertilization or asexual growth. Therefore if a plant 

 of ebenoides should arise from a prothallus of ebeneum or Campto- 

 sorus, ebenoides must be a hybrid. Moreover, the characters of 

 ebeneum and Camptosorus are such that a hybrid between the two, 

 even should it prove unlike ebenoides, must be plainly distinguish- 

 able from plants of pure species of either fern. And the same is 

 true of Aspidium cristatum x marginale and its supposed parents, 

 marginale and cristatum. This fifth method offers, then, a good 

 way of obtaining positive proof of the hybridity or non-hybridity of 

 Asplenium ebenoides and Aspidium cristatum x marginale. It of- 

 ers, also, more certainty of success than any of the other methods, 

 whether the missing organs are reproduced or not, since before that 

 could occur, cross-fertilization would probably take place. 



In December, 1898, with a view to testing the alleged hybridity 

 of Aspidium cristatum x marginale, I sowed in separate flower pots 

 spores of marginale and of cristatum, first sterilizing the earth to 

 destroy all alien spores. The following July, the resultant prothalli 

 had grown sufficiently large to be divided. I then cut and 

 planted archegonial sections of cristatum in another pot, and a 

 week or so later, about the 5th of August, pressed close against 

 them, antheridial sections of marginale. The sections grew and 

 branched. In the conglomeration resulting, it was soon impos- 

 sible to tell which prothalli belonged to marginale and which to 

 cristatum. On the iyth of October, a plant developed, followed 

 before December i3th by several others. Three of these survived. 

 One of the three grew from a segment of a prothallus cluster. Pivy 

 months afterward, in May, 1900, seven more plants developed from 



