134 Danoin on the Effects of Cross- and Self-Fertilizatwn. 



\ 

 precious of all the elements for the growth of plants— but in the 

 case of most open flowers, a large quantity of pollen is consumed 

 liy pollen-devouring insects, and a large quantity is destroyed 

 during long-continued rain. With many plants this latter evil is 

 guarded against, as far as is possible, \>\ the anthers opening only 

 during dry weather, by the position and form of some or all of 

 the petals", by the presence of hairs, etc. ; also, as Kerner has 

 shown in his interestinu' e-sav, by the movements of the petals or 

 of the whole flower during cold and wet weather. In order to 

 compensate the loss of pollen in so many ways, the anthers pro- 

 duce a far larger amount than is necessary for the fertilization of 

 the same flower. I know this from my own experiments on 

 Ipomcea, given in the Introduction ; and it is still more plainly 

 shown by the astonishingly small quantity produced by cleisto- 

 gene flowers, which lose none of their pollen, in comparison with 

 that produced by the open flowers borne bv the same plants; and 

 yet this small quantity suffices for the fertilization of all their 



ber of pollen-grains produced by a flower of the Dandelion, and 

 found the number to be 243,600, and in a Pasony 3,654,000 grains. 

 The editor of the 'Botanical Register' counted the ovules in the 

 flowers of Wisteria sinensis, and carefully estimated the number 

 of pollen-grains, and he found that for each ovule there were 7,000 

 grains." (pp. 376, 377.) 



These are probably fair averages of the numerical ratio of 

 pollen to ovules in flowers which are adapted to be fertilized 

 by insect agency. Their meaning in " the economy of nature " 

 is seen by a comparison on the one hand with ahem^/iu^ns, 

 i. e., wind-fertilized, flowers, in most of which there is a vastly 

 -proportion between the numbers — compensating for 

 inevitable waste — and on the other with cleistogenous flowers, 

 namely those small and le^s developed blossoms which some 

 plants produce in addition to the ordinary sort, and which fer- 

 t were in the bud, necessarily by their own pollen. 

 Here is no waste, and accordingly the anthers are very small, 

 and the pollen-grains not many times more than the ovules : 

 also such flowers are never brightly colored, never odoriferous, 

 and they never secrete nectar. 



The only advantages of this close-fertilization which we can 

 think of are sureness and strict likeness ; both of which are 

 quite as well secured by budding-reproduction. Now, as 

 cleistogene flowers are borne, we believe, chiefly and perhaps 

 only, by species whose normal blossoms are adapted for insect- 

 fertilization, they must be regarded as a subsidiary arrange- 

 ment, a safeguard against failure of proper insect-'. 

 As the volume before us amply shows, this failure is in general 

 provided for by a more or less wide margin of self-fertilization 



