144 TEOr^EOLUM MINUS. Chap V 



leaves; the crossed averaged 13-46, and the self-fertilised 11 '07 

 inches in height, or as 100 to 82. Five months later they were 

 again measured in the same manner, and the results are given 

 in the preceding table. 



The seven crossed plants now averaged 22 -35, and the seven 

 self-fertilised 16 "62 inches in height, or as 100 to 74. But from 

 the great inequality of the several plants, the result is less trust- 

 worthy than in most other cases. In Pot II. the two self- 

 fertilised plants always had an advantage, except whilst quite 

 young, over the two crossed plants. 



As I wished to ascertain how these plants would behave 

 during a second growth, they were cut down close to the ground 

 whilst growing freely. The crossed plants now showed their 

 superiority in another way, for only one out of the seven was 

 killed by the operation, whilst three of the self-fertilised plants 

 never recovered. There was, therefore, no use in keeping any of 

 the plants excepting those in Pots I. and III. ; and in the 

 following year the crossed plants in these two pots showed during 

 their second growth nearly the same relative superiority over 

 the self-fertilised plants as before. 



Trop^olum minus. 



The flowers are proterandrous, and are manifestly adapted 

 for cross-fertilisation by insects, as shown by Sprengel and 

 Delpino. Twelve flowers on some plants growing out of doors 

 were crossed with pollen from a distinct plant and produced 

 eleven capsules, containing altogether twenty-four good seeds. 

 Eighteen flowers were fertilised with their own pollen and 

 produced only eleven capsules, containing twenty-two good 

 seeds ; so that a much larger proportion of the crossed than of 

 the self-fertilised flowers produced capsules, and the crossed 

 capsules contained rather more seed than the self-fertilised in 

 the ratio of 100 to 92. The seeds from the self-fertilised capsides 

 were however the heavier of the two, in the ratio of 100 to 87. 



Seeds in an equal state of germination were planted on the 

 opposite sides of four pots, but only the two tallest plants on 

 each side of each pot were measured to the tops of their stems. 

 The pots were placed in the greenhouse, and the plants trained 

 up sticks, so that they ascended to an unusual height. In three 

 of the pots the crossed plants flowered first, but in the fourth 

 at the same time with the self-fertilised. When the seedlings 

 were between 6 and 7 inches in height, the crossel began to 



