202 NATURAL SCIENCE. March. 



very interesting one recently discovered by Treub in the case of the 

 Casuarineae ; but as that has already been fully described in these 

 columns/ we will not further allude to it. Much greater variation 

 exists in the phenomena connected with pollination, or the carriage 

 of the pollen-grains to the stigma. 



There is no more fertile source of error than the too rigid or too 

 universal application of general laws. It is perfectly true that 

 Nature " works not by partial, but by general laws." But a natural 

 law is not, as some seem to suppose, an external force which directs 

 the phenomena of life, it is simply a generalising of the phenomena 

 themselves. A certain course of proceeding is of advantage to a 

 particular organism or set of organisms ; in other words, they are 

 governed by a general law ; but in some special case the same 

 end is best attained by other means, and we find what is generally 

 termed an exception to the general law. In no department of 

 physiological botany is this \'ariation more strikingly exhibited 

 than in the phenomena of pollination. It was in 1793 that 

 Christian Konrad Sprengel's celebrated work Das entdcchte Gehcimniss 

 der Natny iiti Ban und in der Befrnchtimg dev Blniiien was published. 

 Centenaries have been celebrated on more trivial grounds than 

 the appearance of this "epoch-making" work; since in it was 

 first clearly laid down the law that in a large number of flowers 

 the structure and arrangement of the male and female organs render 

 self-pollination almost impossible, understanding by this term the 

 pollination of the stigma by pollen-grains from anthers in the same 

 flower. It is a matter of general knowledge how greatly this law 

 was exemplified and extended by Darwin and his followers ; but 

 here again the tendency to a too universal application of the law has 

 manifested itself, and during the last few years a remarkable number 

 of observations have been made which indicate that self-pollination 

 is far more general than had at onetime been supposed. The perfume 

 and the bright colour of flowers are undoubtedly important agents in 

 attracting insects to assist in cross-pollination ; and it has been 

 assumed that this must always be their function. But that this is 

 not invariably the case is certain. It has long ago been pointed out 

 that the bee-orchis, Ophrys apifcva, the flower of which so remarkably 

 simulates a bee, is not visited by insects, and yet produces seeds 

 abundantly. Very curious also are the facts in connection with the 

 genus Aristolochia, in which the conspicuous pitcher-shaped perianth 

 has been regarded as a contrivance for attracting insects and ensuring 

 self-pollination. The walls of the pitcher are clothed with woolly or 

 glutinous hairs, which have been assumed to have the function of 

 detaining the pollen brought by the insects which enter the pitchers in 

 great numbers from other flowers, and thus enable them to reach 

 the stigma. W. Burck states, however, as the result of observations 



1 Natural Science, vol. i., p. 132. 



