OiAP. IV. INTERCROSSING OF INDIVIDUALS. 101 



sional cross Avilli a distinct individual being advantageous or 

 indispensable ! 



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

 some otlicr plants, be allowed to seed near eacli other, a large 

 majority, as I have found, of the seedlings thus raised will 

 turn out mongrels : for instance, I raised 233 seedling cab- 

 Ixigcs from some jilants of different varieties growing near 

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

 some even of these were not perfectly true. Yet the pistil of 

 each cabbage-flower is surrounded not only l)y its own six sta- 

 mens, but by those of the many other flowers on the same plant; 

 and the pollen of each flower readily gets on its own stigma 

 without insect-agency ; for I have found that a plant carefully 

 protected produced the full number of pods. How, then, 

 comes it that sucli a vast number of the seedlings are mongrel- 

 ized ? • I suspect that it must arise from the pollen of a distinct 

 varii'tj/ having a prepotent effect over a flower's own pollen ; 

 and that this is part of the general law of good being derived 

 from the intercrossing of distinct individuals of the same spe- 

 cies. When distinct species are crossed the case is directly the 

 reverse, for a jilant's own pollen is almost always prepotent 

 over foreign pollen ; but to this subject Ave shall return in a 

 future chapter. 



In the case of a large tree covered with innumerable flow- 

 ers, 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 tre*, and that flowers on the same tree can be con- 

 sidered as distinct individuals only in a limited sense. I be- 

 lieve this objection to be valid, but that Nature has largely pro- 

 vided 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, we can see that pollen must be regularly carried 

 from flower to flower; and this will give a better chance of 

 ]i()llen being occasionally carried from tree to tree. That trees 

 belonging to all Ord<»rs have their sexes more often separated 

 than other plants, I And to be the case in this country ; and at 

 my request Dr. Hooker tabulated the trees of New Zealand, 

 and Dr. Asa Gray those of the United States, and the result 

 was as I anticipated. On the other hand. Dr. Hooker has re- 

 cently informc(l me that he flnds that the rule does not hold in 

 Australia ; and I have made these few remarks on the sexes of 

 trees simply to call attention to the subject. 



