338 CONCLUDING EEMAKKS Chap. Vin. 



to prevent the fertilisation of the perfect flowers. I do 

 not doubt that this holds good to a certain limited extent, 

 but the production of a large supply of seeds with little 

 consumption of nutrient matter or expenditure of vital 

 force is probably a far more efficient motive power. 

 The whole flower is much reduced in size : but what 

 is much more important, an extremely small quantity 

 of pollen has to be formed, as none is lost through the 

 action of insects or the weather ; and pollen contains 

 much nitrogen and phosphorus. Von Mohl estimated 

 that a single cleistogamic anther-cell of Oxalis aceto- 

 sella contained from one to two dozen pollen-grains ; 

 we will say 20, and if so the whole flower can have 

 produced at most 400 grains; with Impatiens the 

 whole number may be estimated in the same manner 

 at 250 ; with Leersia at 210 ; and with Viola noma 

 at only 100. These figures are wonderfi^lly low com- 

 pared with the 243,600 pollen-grains produced by a 

 flower of Leontodon, the 4,863 by an Hibiscus, or the 

 3,654,000 by a Paeony.* We thus see that cleisto- 

 gamic flowers produce seeds with a wonderfully small 

 expenditure of pollen ; and they produce as a general 

 rule quite as many seeds as the perfect flowers. 



That the production of a large number of seeds is 

 necessary or beneficial to many plants needs no evi- 

 dence. So of course is their preservation before they 

 are ready for germination ; and it is one of the many 

 remarkable peculiarities of the plants which bear 

 cleistogamic flowers, that an incomparably larger pro- 

 portion of them than of ordinary plants bury their 

 young ovaries in the ground ; — an action which it 

 may be presumed serves to protect them from being 



* The authorities for these statements are given in my ' Effects of 

 Cross and Self-Fertilisation,' p. 376. 



