428 
DARWINISM 
CHAP. 
elements, and in this way may profoundly modify the whole 
organisation. Why and how the external effects are limited 
to special details of the structure we do not know ; but it does 
not seem as if any far-reaching conclusions as to the cumula¬ 
tive effect of external conditions on the higher terrestrial 
animals and plants, can be drawn from such an exceptional 
phenomenon. It seems rather analogous to those effects of 
external influences on the very lowest organisms in which the 
vegetative and reproductive organs are hardly differentiated, 
in which case such effects are doubtless inherited. 1 
Professor Geddes's Theory of Variation in Plants. 
In a paper read before the Edinburgh Botanical Society in 
1886 Mr. Patrick Geddes laid down the outlines of a funda¬ 
mental theory of plant variation, which he has further ex¬ 
tended in the article “Variation and Selection” in the 
Encyclopaedia Britannica, and in a paper read before the Linnsean 
Society but not yet published. 
A theory of variation should deal alike with the origin of 
specific distinctions and with those vaster differences which 
characterise the larger groups, and he thinks it should answer 
such questions as— How an axis comes to be arrested to form 
a flower ? how the various forms of inflorescence were evolved ? 
how did perigynous or epigynous flowers arise from hypogynous 
flowers l and many others equally fundamental. Natural selec¬ 
tion acting upon numerous accidental variations will not, he 
urges, account for such general facts as these, which must 
depend on some constant law of variation. This law he 
believes to be the well-known antagonism of vegetative and 
reproductive growth acting throughout the whole course of 
plant development; and he uses it to explain many of the 
most characteristic features of the structure of flowers and 
fruits. 
1 I n Dr. Weismann’s essay on “ Heredity,” already referred to, lie considers 
it not improbable that changes in organisms produced by climatic influences 
may be inherited, because, as these changes do not affect the external parts 
of an organism only, but often, as in the case of warmth or moisture per¬ 
meate the whole structure, they may possibly modify the germ-plasm 
itself, and thus induce variations in the next generation. In this way, lie 
thinks, may possibly be explained the climatic varieties of certain butterflies, 
and some other changes which seem to be effected by change of climate in a 
few generations. 
