218 REVIEWS. 



for its dissemination." That the crossing is beneficial, and 

 consequently the want of it injurious, is a teleological infer- 

 ence from the prevalence of the arrangements which promote 

 or secure it, — an inference the value of which increases with 

 the number, the variety, and the effectiveness of the arrange- 

 ments for which no other explanation is forthcoming. That 

 the good consisted in a re-invigoration of progeny, or the evil 

 of close-breeding in a deterioration of vigor, was the sugges- 

 tion first made (so far as we know), or first made prominent, 

 by Knight, from whom Darwin adopted it. However it be as 

 to animals, there was until now no clear and direct evidence 

 that cross-fertilization in the vegetable kingdom did re-invigo- 

 rate. Indeed, the contrary might be inferred from the long 

 and seemingly indefinite perpetuation of bud-propagating 

 varieties, which have no fertilization at all. But the inference 

 from this is not as cogent as would at first appear. For, 

 although bud-propagation is, we think, to be considered as the 

 extreme of close-breeding, yet in it the amount of material 

 contributed by parent to offspring is usually vastly more than 

 in sexual reproduction ; and, accordingly, the diminution to 

 an injurious degree of any inherited quality or essence might 

 be correspondingly remote. Yet, as sexual reproduction may 

 be and often must be much closer in plants than it can be in 

 most animals, the ill effects of self-fertilization, or the good 

 of cross-fertilization, might the sooner be noticeable. Mr. 

 Darwin arranged a course of experiments to test this question, 

 prosecuted it as to some species for eleven years ; and the main 

 object of this volume is to set forth the results. 



Ipomo&a purpurea, the common Morning Glory of our 

 gardens, was the leading subject. The flowers of this species 

 self-fertilize, but must also be habitually cross-fertilized, as 

 they are visited freely by bumble-bees and other insects. Ten 

 flowers of a plant in a green-house were fertilized with their 

 own pollen ; ten others were crossed with pollen from a dif- 

 ferent plant. The seeds from both were gathered, allowed to 

 germinate on damp sand, and as often as pairs germinated at 

 the same time the two were planted on opposite sides of the 

 same pot, the soil in which was well mixed, so as to be uniform 



