330 BOTANY. [ch. xvi. 



Self- Fertilisation, published in 1876, is one of his most im- 

 portant works, and at the same time one of the most un- 

 readable to any but the professed naturalist. Its value lies 

 in the proof it offers of the increased vigour given to the 

 offspring by the act of cross-fertilisation. It is the comple- 

 ment of the Orchid book because it makes us understand 

 the advantage gained by the mechanisms for insuring cross- 

 fertilisation described in that work. 



The book is also valuable in another respect, because it 

 throws light on the difficult problems of the origin of sex- 

 uality. The increased vigour resulting from cross-fertilisa- 

 tion is allied in the closest manner to the advantage gained 

 by change of conditions. So strongly is this the case, that 

 in some instances cross-fertilisation gives no advantage to 

 the offspring, unless the parents have lived under slightly 

 different conditions. So that the really important thing is 

 not that two individuals of different blood shall unite, but 

 two individuals which have been subjected to different con- 

 ditions. We are thus led to believe that sexuality is a 

 means for infusing vigour into the offspring by the coales- 

 cence of differentiated elements, an advantage which could 

 not accompany asexual reproductions. 



It is remarkable that this book, the result of eleven years 

 of experimental work, owed its origin to a chance observa- 

 tion. My father had raised two beds of Linaria vulgaris 

 one set being the offspring of cross and the other of self- 

 fertilisation. The plants were grown for the sake of some 

 observations on inheritance, and not with any view to cross- 

 breeding, and he was astonished to observe that the offspring 

 of self -fertilisation were clearly less vigorous than the others. 

 It seemed incredible to him that this result could be due to 

 a single act of self-fertilisation, and it was only in the fol- 

 lowing year, when precisely the same result occurred in the 

 case of a similar experiment on inheritance in carnations, 

 tha this attention was " thoroughly aroused," and that he de- 

 termined to make a series of experiments specially directed 

 to the question. 



The volume on Forms of blowers was published in 1877, 

 and was dedicated by the author to Professor Asa Gray, " as 

 a small tribute of respect and affection." It consists of 

 certain earlier papers re-edited, with the addition of a 

 quantity of new matter. The subjects treated in the book 

 are: 



(i.) Heterostyled Plants. 



