CHAP, iv.] REPRODUCTION OF PLANTS. 135 



each other, the power of self-fertilization is retained, and 

 this is the most general mode, although the presence of 

 colour, and in some cases of nectar also, attracts insects 

 which undoubtedly do in many instances effect cross- 

 fertilization. 



The old method of securing cross-fertilization by 

 completely arresting the development of the stamens in 

 all the flowers on one tree and all the pistils in those of 

 another, is modified in most Angiosperms, who have 

 fallen back on the primitive hermaphrodite type of 

 flower, and by a double series of changes have succeeded 

 in preventing self-fertilization and secured the advan- 

 tages of cross-fertilization. Some of the most pronounced 

 contrivances for preventing self-fertilization are to be 

 found amongst our common wild flowers ; perhaps the 

 most general arrangement is in the stamens becoming 

 mature and shedding their pollen before the ovules of 

 the same flower are ready for fertilization, and this in 

 the majority of instances is the only thing absolutely 

 guarded against, although the pollen from one plant 

 must in many instances be conveyed by insects to the 

 stigmas of flowers belonging to a different plant of the 

 same kind, and thus effect cross- fertilization between 

 two distinct individuals. Flowers having the stamens 

 mature before the pistil are said to be proterandrous ; 

 examples, the geraniums, pinks, willow-herbs, and in fact 

 most flowers that have both stamens and pistil. In 

 comparatively few flowers the pistil is mature before the 

 stamens, as in the arum, figwort (Scrophularia nodosa), 

 plantain, etc.; such flowers are termed proterogynous . 

 In other examples the difference in position of the 

 stamens and pistil in the flowers of different individuals 



