Autogamy and Geitonogamy 415 
vigour, but the crossing considerably increases the plant’s capacity 
for flower-production, and the seedlings from such a mother-plant 
are more fertile. 
The conception implied by the term crossing requires a closer 
analysis. As in the majority of plants, a large number of flowers are 
in bloom at the same time on one and the same plant, it follows that 
insects visiting the flowers often carry pollen from one flower to 
another of the same stock. Has this method, which is spoken of as 
Geitonogamy, the same influence as crossing with pollen from another 
plant? The results of Darwin’s experiments with different plants 
(Ipomoea purpurea, Digitalis purpurea, Mimulus luteus, Pelar- 
gonium, Origanum) were not in complete agreement; but on the 
whole they pointed to the conclusion that Geitonogamy shows no 
superiority over self-fertilisation (Autogamy). Darwin, however, 
considered it possible that this may sometimes be the case. “The 
sexual elements in the flowers on the same plant can rarely have 
been differentiated, though this is possible, as flower-buds are in one 
sense distinct individuals, sometimes varying and differing from one 
another in structure or constitution®.” 
As regards the importance of this question from the point of view 
of the significance of cross-fertilisation in general, it may be noted 
that later observers have definitely discovered a difference between 
the results of autogamy and geitonogamy. Gilley and Fruwirth 
found that in Brassica Napus, the length and weight of the fruits as 
also the total weight of the seeds in a single fruit were less in the 
case of autogamy than in geitonogamy. With Sinapis alba a better 
crop of seeds was obtained after geitonogamy, and in the Sugar Beet 
the average weight of a fruit in the case of a self-fertilised plant was 
0009 gr., from geitonogamy 0°012 gr., and on cross-fertilisation 
0°013 gr. 
On the whole, however, the results of geitonogamy show that the 
favourable effects of cross-fertilisation do not depend simply on the 
fact that the pollen of one flower is conveyed to the stigma of another. 
But the plants which are crossed must in some way be different. If 
plants of Ipomoea purpurea (and Mimulus luteus) which have been 
self-fertilised for seven generations and grown under the same con- 
ditions of cultivation are crossed together, the plants so crossed 
would not be superior to the self-fertilised; on the other hand 
crossing with a fresh stock at once proves very advantageous. The 
favourable effect of crossing is only apparent, therefore, if the parent 
plants are grown under different conditions or if they belong to 
1 Similarly crossing in the case of flowers of Pelargonium zonale, which belong to plants 
raised from cuttings from the same parent, shows no superiority over self-fertilisation. 
® Cross and Self fertilisation (1st edit.), p. 444. 
