202 NATURAL SCIENCE. Marcu, 
very interesting one recently discovered by Treub in the case of the 
Casuarinee ; 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 variation more strikingly exhibited 
than in the phenomena of pollination. It was in 1793 that 
Christian Konrad Sprengel’s celebrated work Das entdeckte Geheimniss 
dey Natur im Bau und in dey Befruchtung dey Blumen 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 one time 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 apifera, 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 Avistolochia,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. 
