310 BOTANY. [Ch. XVI. 



tlie Miillers, did not begin to appear until about 1867. The 

 period during which the new views were being assimilated, 

 and before they became thoroughly fruitful, was, however, 

 surprisingly short. The later activity in this department may 

 be roughly gauged by the fact that the valuable ■ Bibliography/ 

 given by Professor D'Arcy Thompson in his translation of 

 Muller's Befruchtung (1883),* contains references to 814 papers. 



In 1877 a second edition of the Fertilisation of Orchids was 

 published, the first edition having been for some time out of 

 print. The new edition was remodelled and almost rewritten, 

 and a large amount of new matter added, much of which the 

 author owed to his friend Fritz Muller. 



With regard to this edition he wrote to Dr. Gray : — 



" I do not suppose I shall ever again touch the book. After 

 much doubt I have resolved to act in this way with all my 

 books for the future ; that is to correct them once and never 

 touch them again, so as to use the small quantity of work left 

 in me for new matter." 



One of the latest references to his Orchid-work occurs in a 

 letter to Mr. Bentham, February 16, 1880. It shows the amount 

 of pleasure which this subject gave to my father, and (what is 

 characteristic of him) that his reminiscence of the work was 

 one of delight in the observations which preceded its publica- 

 tion, not to the applause which followed it : — 



11 They are wonderful creatures, these Orchids, and I some- 

 times think with a glow of pleasure, when I remember making 

 out some little point in their method of fertilisation." 



The Effect of Cross-and Self-fertilisation in the Vegetable King- 

 dom. Different Forms of Flowers on Plants of the same 

 species. 



Two other books bearing on the problem of sex in plants 

 require a brief notice. The Effects of Cross-and Self-Fertili- 

 sation, published in 1876, is one of his most important works, 

 and at the same time one of the most unreadable 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 complement 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 sexuality. 



* My father's * Prefatory Notice " to this work is dated February 6th, 

 1882, and i* therefore almost the last of his writings. 



