24 INTRODUCTORY EEMARKS. Chap. I. 



struck. Some of these causes of error will also have 

 been eliminated by the seeds having been allowed to 

 germinate on bare damp sand, and being planted in 

 pairs ; for it is not likely that ill-matured and well- 

 matured, or diseased and healthy seeds, would germi- 

 nate at exactly the same time. The same result will 

 have been gained in the several cases in which only a 

 few of the tallest, finest, and healthiest plants on each 

 side of the pots were measured. 



Kolreuter and Gartner* have proved that with some 

 plants several, even as many as from fifty to sixty, 

 pollen-grains are necessary for the fertilisation of all 

 the ovules in the ovarium. Naudin also found in 

 the case of Mirabilis that if only one or two of its 

 very large pollen-grains were placed on the stigma, 

 the plants raised from such seeds were dwarfed. 

 I was therefore careful to give an amply sufficient 

 supply of pollen, and generally covered the stigma 

 with it ; but I did not take any special pains to place 

 exactly the same amount on the stigmas of the self- 

 fertilised and crossed flowers. After having acted in 

 this manner during two seasons, I remembered that 

 Gartner thought, though without any direct evidence, 

 that an excess of pollen was perhaps injurious ; and it 

 has been proved by Spallanzani, Quatrefages, aud 

 Newport,f that with various animals an excess of the 

 seminal fluid entirely prevents fertilisation. It was 

 therefore necessary to ascertain whether the fertility of 

 the flowers was affected by applying a rather small and 

 an extremely large quantity of pollen to the stigma. 

 Accordingly a very small mass of pollen-grains was 



* Kenntaiss der Befiuch- torn. i. p. 27. 

 tung,' 1844, p. 345. Naudin, f 'Transactions Philosophical 



4 Nouvelles Archives du Museum,' Soc.' 1853, pp. 253-258. 



