FERN GENERATION, NORMAL AND ABNORMAL. 



253 



two generations are combined in one. Dr. Stansfield's case is 

 that of a crested Lastrea, in which apospory and apogamy are 

 conjoined, the fronds forming a fringe of prothalli and the 

 prothalli budding out into fronds. 



I now show a slide prepared from Prof. F. 0. Bower's 

 diagram of life cycles, showing how the normal cycle of fern — 

 spore, prothallus, sexual action, fern — has been found to vary 

 in the light of the discoveries already cited, but which can now 

 be extended by Mr. Lang's discovery on two British species, that 

 sporangia, or spore heaps, are actually sometimes produced on 

 the prothallus itself, cutting out the fern proper altogether, 

 just as correlated apospory and apogamy shorten the cycle in 

 another way. 



We have now seen that variation plays its part in the genesis 

 of as well as in the form of ferns, as it does in all other things 

 in nature. We also see that the hard and fast line of alterna- 

 tion of generation, presumed to characterise all ferns, has been 

 broken through in numerous instances. As no less than five of 

 these cases, involving four British species, first came under my 

 own notice in my very limited collection, it is a fair presumption 

 that the phenomenon is not extremely rare, and that the exotic 

 species, if studied, would yield many more examples. 



The faculty ferns possess of varying widely in their progeny 

 is a factor I cannot ignore in a paper like this, especially as the 

 knowledge acquired of their genesis has led to some very 

 remarkable results in the way of crossing and hybridising. 

 Mr. E. J. Lowe has produced some very extraordinary hart's- 

 tongues by sowing the spores of widely different forms together, 

 and he and others have amply demonstrated that under some 

 circumstances, not yet so clearly understood as they ought to be, 

 the antherozoids of one prothallus find their way to the arche- 

 gonia of another, the results being a fern showing the compound 

 characters of two parents. Mr. Lowe has satisfied himself that 

 the characters of several varieties may become blended in one 

 prothallus, and has exhibited plants showing the blend clearly 

 enough of some five or six different varieties. The moot point 

 is whether this is arrived at by one crossing, i.e. whether the 

 archegonium is capable of being fertilised from several sources 

 instead of only one, and this the biologist cannot see his way 

 so far to accept unreservedly. Simple crossing, however, is an 



c 



