Self-fertilisation 421 
While the influence of the work on the biology of flowers was 
extraordinarily great, it could not fail to elicit opinions at variance 
with Darwin’s conclusions. The opposition was based partly on 
reasons valueless as counter arguments, partly on problems which 
have still to be solved; to some extent also on that tendency against 
teleological conceptions which has recently become current. This 
opposing trend of thought is due to the fact that many biologists 
are content with teleological explanations, unsupported by proof ; 
it is also closely connected with the fact that many authors estimate 
the importance of natural selection less highly than Darwin did. 
We may describe the objections which are based on the wide- 
spread occurrence of self-fertilisation and geitonogamy as of little 
importance. Darwin did not deny the occurrence of self-fertilisation, 
even for a long series of generations; his law states only that 
“Nature abhors perpetual self-fertilisation’.” An exception to this 
rule would therefore occur only in the case of plants in which the 
possibility of cross-pollination is excluded. Some of the plants with 
cleistogamous flowers might afford examples of such cases. We have 
already seen, however, that such a case has not as yet been shown to 
occur. Burck believed that he had found an instance in certain 
tropical plants (Anonaceae, Myrmecodia) of the complete exclusion 
of cross-fertilisation. The flowers of these plants, in which, however, 
—in contrast to the cleistogamous flowers—the corolla is well 
developed, remain closed and fruit is produced. 
Loew? has shown that cases occur in which cross-fertilisation 
may be effected even in these “cleistopetalous” flowers: humming 
birds visit the permanently closed flowers of certain species of 
Nidularium and transport the pollen. The fact that the formation 
of hybrids may occur as the result of this shows that pollination may 
be accomplished. 
The existence of plants for which self-pollination is of greater 
importance than it is for others is by no means contradictory to 
Darwin’s view. Self-fertilisation is, for example, of greater im- 
portance for annuals than for perennials as without it seeds might 
fail to be produced. Even in the case of annual plants with small 
inconspicuous flowers in which self-fertilisation usually occurs, such 
as Senecio vulgaris, Capsella bursa-pastoris and Stellaria media, 
A. Bateson? found that cross-fertilisation gave a beneficial result, 
1 It is impossible (as has been attempted) to express Darwin’s point of view in a single 
sentence, such as H. Miiller’s statement of the ‘‘ Knight-Darwin law.’ The conditions of 
life in organisms are so various and complex that laws, such as are formulated in physics 
and chemistry, can hardly be conceived. 
2 EB, Loew, ‘‘ Bemerkungen zu Burck..,,” Biolog. Centralbl. xxv1. (1906). 
3 Anna Bateson, “ The effects of cross-fertilisation on inconspicuous flowers,” Annals of 
Botany, Vol. 1. 1888, p. 255. 
