— 6— 



Leaving the subject of variation here, let us consider briefly 

 the probabilities of hybridity among ferns in nature. That 

 hybridity among ferns in nature does sometimes occur we have 

 some convincing evidence, but the difficulties in the way of its 

 accomplishment are so great, and the possibilities of overcoming 

 those difficulties are so remote, that its occurrence must neces- 

 sarily be exceedingly rare. That it may be, and has been brought 

 about through the culture of mixed fern spores seems to have 

 been fairly well proven by the experiments of Lowe, and others. 

 But in sowing a mixture of fern spores for cultivation one is able 

 to confine the field of operation within a very limited and closely 

 guarded area, so that the resultant prothallia are brought into 

 close contact and their intercrossing is rendered comparatively 

 easy if not absolutely certain. 



It is not so, however, in nature. Spores may, as they do, 

 sow themselves by the millions, yet the various agencies by which 

 they are scattered about and dissipated throughout the unlimited 

 space of the open make the blending of the prothalli from differ- 

 ent species altogether a thing of chance, and that chance is not 

 likely to repeat itself very often. It is not with ferns as with 

 flowering plants, where the pollen from one blossom blown about 

 by the wind, or transported by insects, is almost sure to fall upon 

 some other flower, where the organs of fertilization are exposed 

 and fertilize it ; the spores of ferns never fertilize anything, and 

 if they do not germinate themselves, perish altogether. When 

 fern spores do germinate they produce an entirely different plant 

 organism from the fern plant by which they are themselves pro- 

 duced, and the plant organisms, which we call prothalli, develop 

 from their own substance the special fertilizing organs by means 

 of which the reproduction of the fern plant is brought about. 



It is now very well known that fern prothalli sometimes pro- 

 duce proliferous buds from which young fern plants may be de- 

 veloped without the intervention of fertilization exactly as on the 

 laminae or apices of fern fronds — a fact first observed by Dr. 

 Farlow ; and now more recently it has been shown that under 

 certain conditions, the prothalli of some species develop a cylin- 

 drical process that bears sporangia with spores, although it is not 

 yet known whether such spores are capable of germination or 

 not. But as a rule, fern prothalli are either monoecious in char- 

 acter, or dioecious, and fertilization is more likely to take place 

 in the former than in the latter, which are not likely to be- 



