FERTILIZATION IN THE VEGETABLE KINGDOM. 225 



tile. This was not the case in English plants, which, when 

 covered by a net, set a considerable number of capsules, the 

 seeds of which, by weight, were as 71 to 100 of those on 

 plants intercrossed by bees. These Brazilian seeds, sent to 

 England, yielded plants with moderately self-fertile flowers, 

 and this limited self-fertility was increased in two generations 

 of English growth. Conversely, seeds from English plants 

 orown in Brazil were more self-fertile than those reared in 

 Brazil for several generations ; yet " one which did not flower 

 the first year, and was thus exposed for two seasons to the 

 climate of Brazil, proved quite self-sterile, like a Brazilian 

 plant, showing how quickly the climate had acted on its sexual 

 constitution." Having observed that certain individuals of 

 Mignonette were self-sterile, Mr. Darwin secured several such 

 plants under separate nets, and by intercrossing these for a 

 few generations, obtained plants which inherited this peculi- 

 arity, so that " without doubt a self -sterile race of Mignonette 

 could easily have been established." 



Nine of the twelve chapters are devoted strictly to the effects 

 of cross and seK-fertilization. The tenth considers the " means 

 of fertilization." Cross-fertilization is favored or ensured by : 

 1, the separation of the sexes ; 2, the maturity of the male 

 and female sexual elements at different periods; 3, dimor- 

 phism, or even trimorphism ; 4, various mechanical contriv- 

 ances ; 5, the more or less complete inefficiency of the flower's 

 own pollen on its stigma, and the prepotency of pollen from 

 any other individual over that from the same plant. We 

 understand that Mr. Darwin is just now occupied in revising 

 and extending his various papers upon these topics, with a 

 view to their publication in a volume. Here he gives a list of 

 plants which, when insects are excluded, are either quite ster- 

 ile or produce less than half the number of seeds yielded by 

 unprotected plants. This is followed by a list of plants which, 

 when protected from insects, are either quite fertile or yield 

 more than half the number of seeds produced by unprotected 

 plants. 



" Each of these lists contains by a mere accident the same 

 number of genera, namely, forty-nine. The genera in the first 



