92 ON TEE INTBRGRC88IN0 



and must habitually be crossed. So it is with the recipro- 

 cally dimorphic and trimorphic plants previously alluded 

 to. How strange are these facts! How strange that the 

 pollen and stigmatic surface of the same flower, though 

 placed so close together, as jf for the very purpose of self- 

 fertilization, should be in so many cases mutually useless 

 to each other? How simply are these facts explained on 

 the view of an occasional cross with a distinct individual 

 being advantageous or indispensable ! 



If several varieties of the cabbage, radish, onion and of 

 some other plants, be allowed to seed near each other, a 

 large majority of the seedling thus raised turn out, as I 

 founds mongrels: for instance, I raised 333 seedling cab- 

 bages from some plants of different varieties growing near 

 each other, and of these only 78 were true to their kind, 

 and some even of these were npt perfectly true. Yet the 

 pistil of each cabbage-flower is surrounded not only by its 

 own six stamens but by those of the many other flowers on 

 the same plant; and the pollen of each flower readily gets 

 on its stigma without insect agency; fur I have found that 

 plants carefully protected from insects produce the full 

 number of pods. How, then, comes it that such a vast 

 number of the seedlings are mongrelized? It must arise 

 from the pollen of a distinct variety having a prepotent 

 effect over the flower's own pollen; and that this is part of 

 the general law of good being derived from the intercross- 

 ing of distinct individuals of the same species. When dis- 

 tinct species are crossed the case is reversed, for a plant's 

 own pollen is almost always prepotent over foreign pollen; 

 but to this subject we shall return in a future chapter. 



In the case of a large tree covered with innumerable 

 flowers, it may be objected that pollen could seldom be 

 carried from tree to tree, and at most only from flower 

 to flower on the same tree; and flowers on the same tree 

 can be considered as distinct individuals onlv in a limited 

 sense. I beheve this objection to be valid, but that nature 

 has largely provided against it by giving to trees a strong 

 tendency to bear flowers with separated sexes. When the 

 sexes are separated, although the male and female flowers 

 may be produced on the same tree, pollen must be regu- 

 larly carried from flower to flower; and this will give 

 a better chance of pollen being occasionally carried from 



