540 Farmer . — On the Structure of a Hybrid Fern , 
of the protoplasm, and I believe we may here fairly ascribe 
it to the effect of the crossing. Although it may be pre- 
mature to speculate on the nature of the processes concerned 
in the production of hybrids, I am convinced that a careful 
study of these organisms will do much to throw light on the 
obscurities of heredity, and perhaps even on the essentials 
of ordinary fertilization. It seems certain that the quality 
which we term heredity, by virtue of which organisms are 
what they are, and what their forbears have been before them, 
must either be associated with definite discrete particles, ids, 
which by a series of kaleidoscopic rearrangements are able 
to form new combinations after the manner imagined by 
Weismann : or else that heredity must depend on the con- 
figuration, physical and molecular, of a substance taken as 
a whole , and its interaction with the other constituents of the 
cell. In the former case, with each generation a new arrange- 
ment of the pre-existent and persistent particles, each 
associated with hereditary qualities, is assumed to occur ; 
in the latter case a new substance must be formed, which, by 
virtue of its constitution as a whole , governs and determines 
the mode of development of the organism. The id-theory 
seems irreconcilable with what we now know of the details of 
fertilization in plants, and at least in some animals. In these, 
what direct evidence we have, tells against the preliminary 
elimination of unlike hereditary units from the sexual cells 
during their course of development, and clearly indicates 
rather an equivalent distribution of substance. But if this is 
really true, even in a few cases, the objective basis of the 
id-theory is clearly destroyed ; for the elimination of half 
the parental ids from each gamete previous to their union, 
forms an essential part of the theoretical structure built up 
and maintained by Weismann and his followers. The case 
of hybrids has been used by the exponents of the id-theory 
to strengthen their case, and preponderating multiplication 
of paternal or maternal ids — the result of an imaginary 
struggle between purely hypothetical combatants — is sup- 
posed to finally account for the resemblance of this or that 
