CHAP. VI. ZEA MAYS. 233 



reacli the stigmas, so that they could not possibly have been 

 self-fertilised. These flowers were crossed with pollen from a 

 distinct plant. Flowers on the self-fertilised plants of the second 

 generation were again self-fertilised. From the two lots of seeds 

 thus obtained, twenty-one crossed and nineteen self- fertilised 

 plants of equal age, and forming the third generation, were raised 

 in fourteen large pots. They were measured when fully grown, 

 and by an odd chance the average height of the two lots was 

 exactly the same, namely, 35 96 inches ; so that neither side had 

 the least advantage over the other. To test this result, all the 

 plants on both sides in ten out of the above fourteen pots were 

 cut down after they had flowered, and in the ensuing year the 

 stems were again measured; and now the crossed plants ex- 

 ceeded by a little (viz., 1-7 inches) the self-fertilised. They were 

 again cut down, and on their flowering for the third time, the 

 self-fertilised plants had a slight advantage (viz., 1 54 inches) 

 over the crossed. Hence the result arrived at with these plants 

 during the previous trials was confirmed, namely, that neither 

 lot had any decided advantage over the other. It may, however, 

 be worth mentioning that the self-fertilised plants showed some 

 tendency to flower before the crossed plants : this occurred with 

 all three pairs of the first generation ; and with the cut down 

 plants of the third generation, a self-fertilised plant flowered 

 first in nine out of the twelve pots, whilst in the remaining three 

 pots a crossed plant flowered first. 



If we consider all the plants of the three generations taken 

 together, the thirty-four crossed plants average 35 '98, and the 

 thirty-four self-fertilised plants 36 '39 inches in height; or as 

 100 to 101. We may therefore conclude that the two lots 

 possessed equal powers of growth ; and this I believe to be the 

 result of long-continued self-fertilisation, together with exposure 

 to similar conditions in each generation, so that all the indivi- 

 duals had acquired a closely similar constitution. 



XXX. GKAMINACE^}. ZBA MAYS. 



This plant is monoecious, and was selected for trial on this ac- 

 count, no other such plant having been experimented on.* It is 



* Hildebrand remarks that male flowers standing above the 



this species eeems at first sight female flowers ; but practically it 



adapted to be fertilised by pollen must generally be fertilised by 



from the same plant, owing to the pollen from another plant, as the 



