1910) HOYT—FERTILIZATION IN FERNS 343 
occur in all groups, this kind of evidence seems entirely inadequate 
to prove the hybrid nature of any individual. While, if all the three 
lines of evidence given above concurred in indicating any single 
form as a hybrid, they would furnish some reason for so regarding 
it, but they would not furnish conclusive proof of its hybridity. 
This proof could be obtained only by producing experimentally 
the form in question from a cross between cells of known parentage. 
The second class of evidence is given in the works of DRUERY (9), 
FARMER (12), Lowe (27), Miss Stosson (46, 47), Hans (16, 17), 
and others. The supposed hybrids described by these authors were 
obtained by planting together spores, prothalli, or parts of prothalli 
of different species and trusting to chance to obtain a cross. Some of 
the resulting offspring were adjudged hybrids because of their appar- 
ently intermediate character between their supposed parents. This 
evidence, while more trustworthy than that considered above, 
is not beyond question. LOWE obtained such various results from 
his sowings of mixed spores that he was led to propose the theory of 
“multiple parentage” to account for all the differences in the off- 
Spring. Maxon (30) lists the three authentic cases of hybridization 
between species as the Phyllitis scolopendrium (Scolopendrium vul- 
gare) X Ceterarch officinarum described by DRUERY (I0, II), the 
Polypodium vulgare elegantissimumX Phlebodium aureum described 
by FarMER (12), and the Polystichum aculeatum X Polystichum 
angulare described by LowE (27) and DRUERY (11). 
DAVENPORT (6) considers the last two cases uncertain and expresses 
no opinion about the first case. He concludes (p. 7): “I do not see 
how we can ever obtain absolute proof of hybridity in nature, because 
it is manifestly impossible for us to observe the process through which 
it is brought about ; nor do I see how we can obtain positive proof 
through mixed sowing, as it is equally impossible for us to determine 
from which species the germinating spores come. It seems to me 
that in all such cases there will always be an element of uncertainty 
that will compel us to rely altogether upon inductive reasoning for 
Our conclusions, which are not always likely to be safe.” 
The best work in this line is that of Miss Stosson (46, 47). By 
planting together portions of the prothalli of the supposed parents, 
She obtained offspring resembling the plants previously described 
