Darwin on the Effects of Gross- and Self- Fertilization. 137 



between them may perhaps be in some degree beneficial ; but it is 

 not probable that it would be nearly so beneficial as a cross be- 

 tween flowers on distinct trees, as we may infer from the ineffi- 

 ciency of pollen taken from plants which have been propagated 

 from the same stock, though growing on separate roots. The 

 number of bees which frequent certain kinds of trees when in full 

 flower is very great, and they may be seen flying from tree to 

 tree more frequently than might have been expected. Neverthe- 



a Horse-chestnut or Lime-tree, an incomparably larger number of 

 flowers mil-; i I iron glit from other flowers on 



should bear in mind that with the Horse-chestnut, for instance, 

 only one or two of the several flowers on the same peduncle pro- 

 duce a seed; and that this seed i- the product of only one out of 

 several ovules within the same ovarium. Now we know from the 

 experiments of Herbert and others that if one flower is fertilized 

 with p„]jeii whirl, is more efficient than that applied to the other 

 flowers on the same peduncle, the latter often drop off; and it is 

 probable that this would occur with many of the self-fertiiized 



fertilized. Ot the flow, - atiimalh pr.'.duee.f bv a greattree.it 

 is almost certain that a large number would be self-fertilized; 

 and if we assume that the tree produced only 500 flowers, and 

 that this number of seeds were requisite to keep up the stock, so 

 that at least one seedling should hereafter struggle to maturity, 

 then a large proportion of the seedlings would necessarily be de- 

 rived from self-fertilized seeds. 1 ; produced 

 50,000 flowers, of which, the self-fertilized dropped off without 

 yielding seeds, then the cross-ic": : Id seeds 

 f the seed- 

 lings would be vigorous from being the product of a cross 

 between distinct individuals. In thi> manner the production of a 

 vast number of flowers, besides serving to entice numerous insects 

 and to com: lental destruction of many flowers 

 »>> spring-frosts or otherwise, would be a very great advantage 

 t" the species; and when we behold <mr orchard-trees covered 

 with a white sheet of bloom in the spring, we should not tai-ely 

 -. s , | „ , x though comparatively 

 little fruit is produced in the autumn." 



The Horse-chestnut is not altogether a well-cliosen example, 

 for in it, as in our Buckeyes, a verv large proportion of the 

 flowers in the thyrsus air- usually male, with barely a vestige of 

 Pistil. These serve, however, to' increase the show, in the man- 

 ner here illustrated, as " f P ollen - 



The section on anemophilous (wind- tort 

 interest as survivals of the earlier phasnogamic vegetation,— 

 the speculation as to how, when flying insects came ti 

 an anemophilous plant may have been rendered entomopbi- 



Am. Joob. Scl, Third Sekies-Vol. XIII, No. 74.— Fbb., 1877. 



