X FLORA OF TASMANIA. 
has so many enemies that they do not perpetuate its race. In the case of annual plants, those only 
can secure the succession of their species which produce more seeds annually than can be eaten by 
animals or destroyed by the elements. Cultivated wheat will grow and ripen its seed in almost all 
soils and climates, and as its seeds are produced in great abundance, and can be preserved alive in 
any quantity, in the same climate, and for many years, it follows that it is not to the artificial or 
peculiar condition of the plant itself, and still less to any change effected by man upon it, that its 
annual extinction is due, but to causes that have no effect whatever upon its own constitution, and 
over which its constitutional peculiarities can exercise no control. 
11. Again, the phenomena of cross impregnation amongst individuals of all species appear, 
according to Mr. Darwin's accurate observations, to have been hitherto much underrated, both as to 
extent and importance. The prominent fact that the stamens and pistil are so often placed in the 
same flower, and come to maturity at the same epoch, has led to the doctrine that flowers are usually 
self-impregnated, and that the effect is a conservative one as regards the permanence of specific 
forms. The observations of Carl Sprengel and others have, however, proved that this is not always 
the case, and that while Nature has apparently provided for self-fertilization, she has often insidiously 
counteracted its operation, not only by placing in flowers lures for insects which cross-fertilize them, 
but often by interposing insuperable obstacles to self-fertilization, in the shape of structural impedi- 
ments to the access of the pollen to the stigma of its own flower.* In all these instances the double 
object of Nature may be traced; for self-impregnation (or "breeding in"), while securing identity 
of form in the offspring, and hence hereditary permanence, at the same time tends to weakness of 
constitution, and hence to degeneracy and extinction : on the other hand, cross-impregnation, while 
tending to produce diversity of form in the offspring, and hence variation and apparent mutability, 
yet by strengthening the offspring favours longevity and apparent permanence of specific type. The 
ultimate effect of all these operations is of course favourable to the hypothesis that variability is the 
rule, and permanence the exception, or at any rate only a transitory phenomenon. 
12. Hybridization, or cross-impregnation between species or very well marked varieties, again, 
is a phenomenon of a very different kind, however similar it may appear in operation and analo- 
gous in design. Hybridizable genera are rarer than is generally supposed, even in gardens, where 
they are so often operated upon, under circumstances the most favourable to the production of a 
hybrid, and unfavourable to self-impregnation. Hybrids are almost invariably barren, and their 
characters are not those of new varieties. The obvious tendency of hybridization between varieties 
or other very closely allied forms (in which case the offspring may be fertile) is not to enlarge the 
bounds of variation, but to contract them; and if between very different forms, it will only tend to 
confound these. That some supposed species may have their origin in hybridization cannot be denied, 
but we are now dealing with phenomena on a large scale, and balancing the tendencies of causes 
uniformly acting, whose effects are unmistakable, and which can be traced throughout the Vegetable 
Kingdom. In gardening operations the number of hybridized genera is small, their offspring 
doomed, and since they are more readily impregnated by the pollen of either parent than by their own, 
* Thus, in Lobelia fulgens, the pollen is entirely prevented by natural causes from reaching the stigma of its 
r. In kidney beans impregnation takes plaee imperfectly except the carina is worked up and down alli- 
es elected by bees, who may thus either impregnate the flower ■ 
brought W another plant. I am indebted to M, Darwin for both these facts : see < Gardeners' Chronicle/ 1858, 
