CHAP. II. SUMMARY OF OBSERVATIONS. 55 



unfortunate circumstance, but my experiments were 

 not thus vitiated, as both lots of plants were exposed 

 to the same conditions, whether favourable or un- 

 favourable. 



There is reason to believe that the flowers of this 

 Ipomoaa, when growing out of doors, are habitually 

 crossed by insects, so that the first seedlings which I 

 raised /rom purchased seeds were probably the offspring 

 of a cross. I infer that this is the case, firstly from 

 humble-bees often visiting the flowers, and from the 

 quantity of pollen left by them on the stigmas of su-ch 

 flowers ; and, secondly, from the plants raised from the 

 same lot of seed varying greatly in the colour of their 

 flowers, for as we shall hereafter see, this indicates 

 much intercrossing.* It is, therefore, remarkable 

 that the plants raised by me from flowers which were, 

 in all probability, self-fertilised for the first time after 

 many generations of crossing, should have been so 

 markedly inferior in height to the intercrossed plants 

 as they were, namely, as 76 to 100. As the plants 

 which were self-fertilised in each succeeding generation 

 necessarily became much more closely interbred in 

 the later than in the earlier generations, it might have 

 been expected that the difference in height between 

 them and the crossed plants would have gone on in- 

 creasing ; but, so far is this from being the case, that 

 the difference between the two sets of plants in the 

 seventh, eighth, and ninth generations taken together 

 is less than in the first and second generations together. 

 When, however, we remember that the self-fertilised 

 and crossed plants are all descended from the same 



* Verlot says (' Sur la Produo- color, cannot be kept pure unless 



tion des Vur^tes,' 1865, p. 66) grown at a distance from all otbei 



that certain varieties of a closely varieties, 

 allied plant, the Convolvulus tri- 



