542 Farmer. — On the Structure of a Hybrid Fern , 
new generation into the sporophyte of the old, whereby 
a particular new form of fruit is stimulated to grow. Nor 
can we assume that the tree had stores of ids requisite to 
produce this or that form of fruit. If we say that the 
pollination stimulated the formation of new arrangements of 
ids, we are going far beyond analogies based on knowledge, 
which would rather suggest chemical interaction, and are simply 
abandoning ourselves to flights of pure fancy. 
And to return to the Fern, I confess I find it almost 
impossible to imagine a machinery complex enough to 
account for the reversions it exhibits on the assumption of 
separate ids, whilst it does not, to me at least, seem so unin- 
telligible on the alternative view. Instances might easily be 
multiplied. Thus Hildebrand 1 found, in a cross between 
Oxalis latifolia and O. tetraphylla , that the characteristically 
distinct hairs of each species might both arise from a single 
epidermal cell of the offspring. Are we in this case to 
imagine that the ids and determinants of the corresponding 
cells in both parents were all actively present in the nucleus 
of this epidermal cell ? And if we answer in the affirmative, 
how shall we explain the further case that amongst the 
offspring obtained by crossing O. lasiandra with O. Andreuxii , 
some of the hybrids possessed flowers readily distinguishable 
from those of either parent, not only on account of their 
larger size, but also in their totally different colour? What, 
we may ask, has become of the action of the individual ids 
here? The frequently observed sterility of hybrids, as well 
as the failure of numerous likely crosses to set seed, may 
be due, quite as well as to an unsuitable consorting of 
ids, to the imperfect combination or union of the parental 
substances, a defect the results of which (whatever its true 
nature may be) are apparent in all degrees and gradations 
varying from positive and absolute sterility on the one hand 
and only stopping short of actual fertility on the other. 
These are only tentative suggestions, for in the present 
1 F. Hildebrand, Ueber einige Pflanzenbastardierungen ; Jen. Zeitschr., Bd. 23, 
