d exhibited before the Royal Agricultural Society[293]
specimens of crossed wheat, together with their parent varieties; and
the editor states that they were intermediate in character, "united
with that greater vigour of growth, which it appears, in the vegetable
as in the animal world, is the result of a first cross." Knight also
crossed several varieties of wheat,[294] and he says "that in the years
1795 and 1796, when almost the whole crop of corn in the island was
blighted, the varieties thus obtained, and these only, escaped in this
neighbourhood, though sown in several different soils and situations."

Here is a remarkable case: M. Clotzsch[295] crossed _Pinus sylvestris_
and _nigricans_, _Quercus robur_ and _pedunculata, Alnus glutinosa_ and
_incana_, _Ulmus campestris_ and _effusa_; and the cross-fertilised
seeds, as well as seeds of the pure parent-trees, were all sown at the
same time and in the same place. The result was, that after an interval
of eight years, the hybrids were one-third taller than the pure trees!

* * * * *

The facts above given refer to undoubted varieties, excepting the trees
crossed by Clotzsch, which are ranked by various botanists as
strongly-marked races, sub-species, or species. That true hybrids
raised from entirely distinct species, though they lose in fertility,
often gain in size and constitutional vigour, is certain. It would be
superfluous to quote any facts; for all experimenters, Koelreuter,
Gaertner, Herbert, Sageret, Lecoq, and Naudin, have been struck with
the wonderful vigour, height, size, tenacity of life, precocity, and
hardiness of their hybrid productions. Gaertner[296] sums up his
conviction on this head in the strongest terms. Koelreuter[297] gives
numerous precise measurements of the weight and height of his hybrids
in comparison with measurements of both parent-forms; and speaks with
astonishment of their "_statura portentosa_," their "_ambitus
vastissimus ac altitudo valde conspicua_." Some exceptions to the rule
in the case of very sterile hybrids have, however, been noticed by
Gaertner and {131} Herbert; but the most striking exceptions are given
by Max Wichura,[298] who found that hybrid willows were generally
tender in constitution, dwarf, and short-lived.

Koelreuter explains the vast increase in