224 REVIEWS. 



and the roots probably came out of the holes at the bottom, 

 and thus aided their growth. Early in the following summer, 

 the superiority of the crossed plants, owing to their increase 

 by stolons, over the self -fertilized plants, was truly won- 

 derful. . . . Both the crossed and the self-fertilized plants 

 being left freely exposed to the visits of bees, manifestly 

 produced much more seed than their grandparents, — the 

 plants of original clumps still growing close by in the same 

 garden, and equally left to the action of bees." 



These few cases must here suffice, and they give a fair gen- 

 eral idea of the main results reached, — somew^hat qualified, 

 however, by certain instances in which little or no benefit 

 was observed. Let it be remarked that while most of the 

 cases show decided and unequivocal good from the crossing, 

 none of them unequivocally tell to the contrary, as the ad- 

 vantage appears sometimes in one direction, sometimes in 

 another. "Thus, the crossed and self - fertilized plants of 

 Ipomsea, Papaver, Reseda odorata, and Limnanthes were 

 almost equally fertile, yet the former exceeded considerably 

 in height the self-fertilized plants. On the other hand, the 

 crossed and seK-fertilized plants of Mimulus and Primula 

 differed in an extreme degree in fertility, but by no means to 

 a corresponding degree in height or vigor." 



We must wholly omit — among many other things — the 

 interesting account of self-sterile plants, meaning here not 

 those in which the pollen does not reach the stigma unaided, 

 but those in which it is impotent, or nearly so, when applied, 

 although efficient upon the stigma of another individual. 

 Verbascum, Passiflora, Corydalis, and many Orchids afford 

 instances of this sort. In these, the advantage of cross-fer- 

 tilization arises to a necessity. A noteworthy fact respect- 

 ing them (of which Mr. Darwin makes much) is, that such 

 self-sterility, or the reverse, is influenced by slight changes 

 in the conditions, such as difference in temperature, grafting 

 on another stock, and the like. In South Brazil, Fritz Miiller 

 found that for six generations all his plants of Eschsclioltzia 

 Californica were completely sterile, unless supplied with 

 pollen from a distinct plant, when they were completely fer- 



