Seedling Saxif images. 229 



unlimited number of generations. Our own Dean Herbert 

 nearly made the same discovery, as he found that advantage 

 was derived from the seed obtained by pollen from another 

 individual of the same variety, rather than its own. Darwin, 

 however, finally showed by careful investigation that plants 

 were improved by crossing with another stock ; that the 

 application of pollen to the pistil of the same flower is less 

 efficient than pollen from another individual. He also 

 showed how frequently self-fertilization is prevented by the 

 relative position of the reproductive organs, or by their 

 ripening at different times. This subject has been carried 

 much further by Miiller, whose book contains minute 

 descriptions of the reproductive parts of every class of 

 flower, and long lists of the insects which are found to 

 frequent each flower in search of food. Miiller, however, 

 does not appear to have observed the saxifrages, and he 

 gives no list of insects frequenting them. He merely states 

 that Dr. A. Engler investigated 38 species of saxifrages, 

 and found them all to be proterandrous ; the pollen-tipped 

 stamens moving singly, in succession, towards the centre of 

 the flower. In this way the pistil became fertilized. This, 

 I find, may readily be observed in many of the saxifrages, 

 and particularly in S. oppositifolia, and there is but little 

 variety in this class of self-fertilized saxifrages. Miiller 

 then remarks that in some Alpine species there is the 

 peculiarity that the anthers are withered before the stigma 

 has ripened. He does not name 6". Cotyledon, or any species 

 having these habits, but herein we have the key to the 

 question before us. 



Julius von Sachs, in his "Physiology of Plants," just trans- 

 lated by Professor Marshall Ward, describes this peculiar 

 arrangement under the term " Dichogamy," i.e., the non- 

 simultaneous development of the two sexual organs. When 

 this occurs, as it does in S. Cotyledon and 5. Macnabiana^ 

 insects are the means by which the pollen is carried to the 

 Q 



