26 INTRODUCTORY REMARKS. CHAP. I. 



species. Another table exhibits the striking results 

 from fertilising plants, which during several generations 

 had either been self-fertilised or had been crossed 

 with plants kept all the time under closely similar 

 conditions, with pollen taken from plants of a distinct 

 stock and which had been exposed to different con- 

 ditions. In the concluding chapters various related 

 points and questions of general interest will be 

 discussed. 



Anyone not specially interested in the subject need 

 not attempt to read all the details; though they 

 possess, I think, some value, and cannot be all sum- 

 marised. But I would suggest to the reader to take 

 as an example the experiments on Ipomoea in Chapter 

 II. ; to which may be added those on Digitalis, Origa- 

 num, Viola, or the common cabbage, as in all these 

 cases the crossed plants are superior to the self- 

 fertilised in a marked degree, but not in quite the 

 same manner. As instances of self-fertilised plants 

 being equal or superior to the crossed, the experiments 

 on Bartonia, Canna, and the common pea ought to be 

 read; but in the last case, and probably in that of 

 Canna, the want of any superiority in the crossed 

 plants can be explained. 



Species were selected for experiment belonging to 

 widely distinct families, inhabiting various countries. 

 In some few cases several genera belonging to the 

 same family were tried, and these are grouped toge- 

 ther ; but the families themselves have been arranged 

 not in any natural order, but in that which was the 

 most convenient for my purpose. The experiments 

 have been fully given, as the results appear to me of 

 sufficient value to justify the details. Plants bearing 

 hermaphrodite flowers can be interbred more closely 

 than is possible with the higher animals, and are there- 



