SEXUAL REPRODUCTION. 



139 



fold devices for ensuring that the unconscious insects carry the 

 fertilising pollen from one flower to another, but has also 

 emphasised the beneficence of cross-fertilisation for the health 

 of the species. "Nature tells us," he says, "in the most 

 emphatic manner that she abhors perpetual self-fertilisation." 

 Hildebrand, Hermann Miiller, Delpino, and others, have, with 

 consummate patience of observation, further traced out the 

 secrets of nature in this relation; and the student may be 

 referred to Professor D'Arcy Thompson's valuable edition of 

 Miiller's " Fertilisation of Flowers," Sir John Lubbock's 

 "Flowers in Relation to Insects," and the classic works of 

 Darwin. Reference must, however, also be made to Meehan's 

 protest (see pp. 75, 76), that self-fertilisation is neither so rare 

 nor so "abhorrent" as is now generally believed. 



Bees visiting White Deadnettle and Broom. 



In a great number of cases, cross-fertilisation by means of 

 insects does occur ; in many it must occur. In another by no 

 means small set of flowering plants, — usually with inconspicuous 

 blossoms, — the fertilising gold dust is borne by the wind, and 

 falls, like the golden shower on Danae, upon adjacent flowers. 

 In many hermaphrodite flowers, again, self-fertilisation does cer- 

 tainly take place ; in some this is necessarily so. Interesting in 

 this connection is the indubitable self-fertilisation which occurs 

 in the small degenerate unopening (cleistogamous) flowers of 

 some plants, such as species of balsam, deadnettle, pansy, &c. 

 These occur along with ordinary flowers, and, curiously enough, 

 are sometimes more fertile than they. 



In most of the lower plants, the male elements are minute, 

 and actively mobile. They find their way through the water, or 



