316 THE STRUCTURE OF FLOWERS. 



the number of seeds produced by the parent plants. With 

 respect to the second of these two propositions, namely, that 

 self-fertilisation is generally injurious, we have abundant 

 evidence. The structure of the flowers in such plants as 

 Lobelia ramosa^ Digitalis purpurea, etc., (1) renders the aid 

 of insects almost indispensable for their fertilisation ; and 

 bearing in mind the prepotency of pollen from a distinct 

 individual over that from the same individual, such plants 

 mil almost certainly have been crossed during many or all 

 previous generations. So it must be, owing merely to the 

 prepotency of foreign pollen, with cabbages and various 

 other plants, the varieties of which almost invariably in- 

 tercross when grown together. The same inference may 

 be drawn still more surely with respect to those plants, such 

 as Reseda (2), and JEschscholtzia (3), which are sterile with 

 •their own pollen, but fertile with that from any other 

 individual. These several plants must therefore have been 

 crossed during a long series of previous generations, and the 

 artificial crosses in my experiments cannot have increased 

 the vigour of the offspring beyond that of their progenitors. 

 Therefore the difference between the self-fertilised and 

 crossed plants raised by me cannot be attributed to the 

 superiority of the crossed, but to the inferiority of the self- 

 fertilised seedlings, due to the injurious effects of self- 

 fertilisation." 



Mr. Darwin then proceeds to discuss the first proposition, 

 " that cross-fertilisation is generally beneficial," so that we 

 may conclude that the preceding quotation represents the 

 author's reasoning and conclusions on the idea of there 

 being some " injuriousness " in self-fertilisation. 



In the first place, it may be observed that the reason 

 why Mr. Darwin's crossings yielded at first more marked 

 results in height, fertility, etc., is because plants are never 



