INTRODUCTION 3 



posed, on authority entitled to the highest respect,^ which altogether 

 abolished the bifurcation into Algae and Fungi. On this system the 

 sole character made use of in their primary' classification was the mode 

 of reproduction. First came the Protophyta, in which no sexual mode 

 of reproduction is known, followed by three primary classes (in ascending 

 order) — the Zygosporeae, Oosporeae, and Carposporeae — distinguished 

 solely by the degree of complexity of the sexual process. Each of these 

 four classes was then divided into a series containing chlorophyll and a 

 series not containing chlorophyll, the former including the organisms 

 hitherto known as Alg^e, the latter those hitherto known as Fungi. 



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 organised forms. In the higher forms of life the mode of 

 sexual reproduction 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 live- 

 lihood, 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 occurrence 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 pro- 

 cess of reproduction there is not the uniformity that might have lieen 

 expected. While such an apparently subordinate point as the number 

 of cotyledons in the embyro 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 receives 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 



' See Sachs's Text-book of Botany, 2nd English edition, p. 244. 



B 2 



