96 THUNBEKGIA ALATA. Chap. III. 



The average height of the crossed plants is here 20 inches, and 

 that of the self-fertilised 17-12 ; or as 100 to 86. But this excess 

 of height by no means gives a fair idea of the vast superiority in 

 vigour of the crossed over the self-fertilised plants. The crossed 

 flowered first and produced thirty flower-stems, whilst the self- 

 fertilised produced only fifteen, or half the number. The pots 

 were then bedded out, and the roots probably came out of the 

 holes at the bottom and thus aided their growth. Early in the 

 following summer the superiority of the crossed plants, owing 

 to their increase by stolons, over the self-fertilised plants was 

 truly wonderful. In Pot I., and it should be remembered that 

 very large pots had been used, the oval clump of crossed plants 

 was 10 by 4| inches across, with the tallest stem, as yet young, 

 5i inches in height ; whilst the clump of self-fertilised plants, 

 on the opposite side of the same pot, was only 3 h by 2 J inches 

 across, with the tallest young stem 4 inches in height. In Pot 

 II., the clump of crossed plants was 18 by 9 inches across, with 

 the tallest young stem 8h inches in height; whilst the clump of 

 self-fertilised plants on the opposite side of the same pot was 12 

 by 41 inches across, with the tallest young stem 6 inches in 

 height. The crossed plants during this season, as during the 

 last, flowered first. Both the crossed and self-fertilised plants 

 being left freely exposed to the visits of bees, manifestly produced 

 much more seed than their grand-parents, the plants of tho 

 original clump still growing close by in the same garden, and 

 equally left to the action of the bees 



V. ACANTHACEjE Thunbergia alata. 



It appears from Hildebrand's description (' Bot. Zeitung,' 1867, 

 p. 285) that the conspicuous flowers of this plant are adapted 

 for cross-fertilisation. Seedlings were twice raised from pur- 

 chased seed; but during the early summer, when first expe- 

 rimented on, they were extremely sterile, many of the anthers 

 containing hardly any pollen. Nevertheless, during the autumn 

 these same plants spontaneously produced a good many seeds. 

 Twenty-six flowers during the two years were crossed with 

 pollen from a distinct plant, but they yielded only eleven 

 capsules; and these contained very few seeds! Twenty-eight 

 flowers were fertilised with pollen from the same flower, and 

 these yielded only ten capsules, which, however, contained 

 rather more seed than the crossed capsules, Eight pairs of 



