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Show 280 DICECIOUS AND 0UAP. VII. This, however, would be effected only under the contino ·ency of a reduced number of seeds, produced by theb females alone, being sufficient to keep up the stock. There is another way of looking at the subject which partially removes a difficulty ~hat appears at ~rst sight insuperable, namely, that dunng the conversion of an hermaphrodite in to a dimcious plant, the male organs must abort in some individuals and the female organs in others. Yet as all are exposed to the same conditions, it might have been expected that those which varied would tend to vary in the sa1ne manner. As a general rule only a few individuals of a species vary simultaneously in the same manner; and there is no i1nprobability in the assumption that some few individuals might produce larger seecls than the average, better stocked with nourishment. If the production of such seeds were highly beneficial to a species, and on this head there can be little doubt,* the variety with the large seeds would tend to increase. But in accordance with the law of conlpensation we 1night expect that the individuals which produced such seeds would, if living under severe conditions, tend to produce less and less pollen, so that their anthers would be reduced in size and n1ight ultiInately become rudimentary. This view occurred to me owing to a statement by Sir J. E. Smith t that there are female and hermaphrodite plants of Serratula tinctoria, and that the seeds of the former are larger than those of the hermaphrodite form. It may also be worth while to recall the case of the mid-styled form of Lythrum salicaria, which produces a larger * See the facts given in ' The Effects of Cross and Self-fertilisa, tion,' p. 353. t ' Trans. Linn. Soc.,' vol. xiii. p. 600. CIIAP. VII. POLYGAMOUS PLANTS. 281 number of seeds than the other forms, and has somewhat smaller pollen-grains which have less fertilising power than those of the corresponding stamens in the other two forms; but whether the large): number of seeds is· the indirect cause of the diminished power of the pollen, or vice ·versa, I know not. As soon as the anthers in a certain number of individuals became reduced in size in the manner just suggested or from any other cause, the other individuals would have to produce a larger supply of pollen; and such increased development would tend to reduce the female organs through the law of compensation, so as ultimately to leave them in a rudimentary condition; and the species would then beco1ne dimcious. Instead of the first change occurring in the female organs we may suppose that the male ones first varied, so that some individuals produced a larger supply of pollen. This would be beneficial under certain circumstances, such as a change in the nature of the insects which visited the flowers, or in their becoming more anemophilous, for such plants require an enormous quantity of pollen. The increased action of the male organs would tend to affect through compensation the female organs of the same flower ; and the final result would be that the species would consist of males and hermaphrodites. But it is of no use considering this case and other analogous ones, for, as stated in the Introduction, the co-existence of 1nale and hermaphrodite plants is excessively rare. It is no valid objection to the foregoing views that changes of such a nature would be effected with extreme slowness, for we shall presently see good reason to believe that various hermaphrodite plants have bec~me or are becoming dimcious by many and excessively small steps. In the case of polygamous |
