x FLORA OF TASilANIA. 



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 chmate, 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-fertihzation, 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, aud 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, aud since they are more readily impregnated by the pollen of either parent than by their own, 



* Thus, in Lobelia fidgem, the pollen is entirely prevented by natural causes from reaching the stigma of its 

 own flower. In kidney beans impregnation takes place imperfectly except the carina is worked up and down arti- 

 ficially, which is effected by bees, who may thus either impregnate the flower with its own pollen or with that 

 brought from another plant, I am indebted to Mr. Darwin for both these facts : see ' Gardeners' Chronicle,' 1858, 

 p. 828. 



