50 MR, A. W. BENNETT ON THE 
In support of this view it was urged, with great plausibility, 
that, reproduction being the most important event in the life- 
history of a plant, the mode in which this is brought about must 
become fixed in each group by heredity ; while such a subordinate 
character as the presence or absence of chlorophyll is seen in the 
higher plants to be entirely without importance in determining 
affinity. But a little consideration will show that it is unsafe to 
apply the same rule to more highly and to less highly organized 
forms. In the higher forms of life the mode of sexual repro- 
duction becomes, in its main features, absolutely fixed; and 
throughout the vast range of Angiosperms—as in the higher 
animals—there is entire uniformity in this respect in all important 
points ; while in external morphology, and in the mode in which 
they obtain their livelihood, there is the greatest diversity, even - 
within a narrow circle of affinity. In the animal kingdom we 
may point, as an illustration of this law, to the existence of such 
a family as the Cetacea among Mammalia; among flowering 
plants we have only to consider such phenomena as the occur- 
rence of parasitism, insectivorous habits, or the suppression of 
chlorophyll, in individual genera dispersed through a large 
number of natural orders. Even in subsidiary characters 
connected with the process of reproduction there is not the 
uniformity that might have been expected. While such an 
apparently subordinate point as the number of cotyledons in the 
embryo is so constant as to give its name to primary divisions of 
Phanerogams, a character which might have been supposed to be 
much more important (but which, it is instructive to observe, is 
connected with the mode in which the germinating embryo re- 
ceives its nutriment)—viz. the presence or absence of endosperm 
—is not always constant, even within narrow limits. The first 
necessity of a nascent organism is to live; and hence it is not 
surprising to find that in the lower forms of life the one character 
Which remains most constant within wide circles of affinity is the 
mode of life. In the course of development of the higher forms, 
Nature may be said to have tried a variety of experiments in the 
mode of reproduction ; on the whole there is a continual advance; 
but still by no means infrequent fallings back to simpler modes ; 
and unless this law of retrogression is taken into account, any 
system of classification must be pro tanto imperfect and mis- 
leading. 
If these considerations have any weight, it is not surprising 
