22 THE FERTILISATION OF FLOWERS. [PART I. 
the much more comprehensive and general law “that no organic 
being fertilises itself for a perpetuity of generations, but that 
a cross with another individual is occasionally—perhaps at very 
long intervals—indispensable.” And, in his exhaustive researches 
on the floral contrivances of orchids, he had always kept in view 
as his chief aim the establishment of this law.! | 
Hildebrand and Delpino followed the same aim just as dis- 
tinctly, though they expressed it in other words.? All three sought 
to explain all the contrivances of flowers, presupposing the accuracy 
of that general law. . If all floral mechanisms without exception 
had turned out to subserve the necessity of occasional cross-fertili- 
sation, the establishment of that law, and with it the foundation of 
our comprehension of flowers, would have attained thereby to the 
highest measure of certainty; but in point of fact, as on the one 
hand more and more flowers were adduced in which cross-fertili- 
sation is, under natural conditions, inevitable, on the other hand, 
in at least equal proportion, more and more instances were revealed 
of plants which regularly fertilise themselves and are fully pro- 
ductive thereupon. Inasmuch as one cannot admit that the mere 
possibility of occasional cross-fertilisation is a sufficient proof of its 
necessity, it must be acknowledged that the establishment of the 
Knight-Darwin law is not advanced in the least by all the 
researches on the mechanism of flowers. The whole explanatory 
theory of flowers, so long as it is based entirely upon this law, has 
this uncertainty at its foundation. 
In order to avoid this uncertainty and to secure a firm basis for 
investigating the conditions determining the forms of flowers, it is 
above all necessary to leave aside the Knight-Darwin law, which 
can neither be proved by investigating the forms of flowers nor is 
necessary for their elucidation; and to confine ourselves to the 
proposition, which is sufficient for this investigation and which 
can be verified by experiment, that cross-fertilisation results in 
offspring which vanquish the offspring of self-fertilisation in the 
struggle for existence. 
1 “In my volume ‘ On the Origin of Species,’ 1 have given only general reasons for 
my belief that it is an almost universal law of nature that organic beings require 
an occasional cross with another individual; or, which is the same thing, that 
no hermaphrodite fertilises itself for a perpetuity of generations, Having been 
blamed for propounding this doctrine without giving ample facts, for which I had not 
in that work sufficient space, I wish to show that I have not spoken without having 
gone into details.”’—Darwin, On the Various Contrivances, ete., p. 1. 
* Hildebrand calls it the law of the avoidance and the disadvantage of continual 
self-fervilisation (*‘ das Gesetz der vermiedenen und unvortheilhaften stetigen Selbst- 
befruchtung’”’); Delpino calls it the great law of dichogamy, or of intercrossing (“la 
gran legge della dicogamia o delle nozze incrociate "), 
ee ee 
