PUBLICATIONS. 



77 



Bell's admirable work on expression, and this greatly increased 

 the interest which I felt in the subject, though I could not at 

 all agree with his belief that various muscles had been spe- 

 cially created for the sake of expression. From this time for- 

 ward I occasionally attended to the subject, both with respect 

 to man and our domesticated animals. My book sold largely; 

 5267 copies having been disposed of on the day of publication. 



In the summer of i860 I was idling and resting near Hart- 

 field, where two species of Drosera abound ; and I noticed 

 that numerous insects had been entrapped by the leaves. I 

 carried home some plants, and on giving them insects saw the 

 movements of the tentacles, and this made me think it proba- 

 ble that the insects were caught for some special purpose. 

 Fortunately a crucial test occurred to me, that of placing a 

 large number of leaves in various nitrogenous and non-nitro- 

 genous fluids of equal density ; and as soon as I found that 

 the former alone excited energetic movements, it was obvious 

 that here was a fine new field for investigation. 



During subsequent years, whenever I had leisure, I pur- 

 sued my experiments, and my book on * Insectivorous Plants ' 

 was published in July 1875 — that is, sixteen years after my 

 first observations. The delay in this case, as with all my 

 other books, has been a great advantage to me ; for a man 

 after a long interval can criticise his own work, almost as well 

 as if it were that of another person. The fact that a plant 

 should secrete, when properly excited, a fluid containing an 

 acid and ferment, closely analogous to the digestive fluid of 

 an animal, was certainly a remarkable discovery. 



During this autumn of 1876 I shall publish on the ' Effects 

 of Cross and Self- Fertilisation in the Vegetable Kingdom.* 

 This book will form a complement to that on the ' Fertilisa- 

 tion of Orchids,' in which I showed how perfect were the 

 means for cross-fertilisation, and here I shall show how im- 

 portant are the results. I was led to make, during eleven 

 years, the numerous experiments recorded in this volume, by 

 a mere accidental observation ; and indeed it required the 

 accident to be repeated before my attention was thoroughly 



