Preface vii 



has been given, and is given, to students to take up physiological 

 botany or to investigate the morphology of such plants as exhibit 

 sufficiently striking peculiarities to arrest the attention even of 

 a casual observer ; but what encouragement is given to a student 

 who wishes to take up the systematics of any group of plants ? 

 The answer is found in the ' Bibliography ' of every work on 

 systematic botany. 



Although the work of the systematist is indispensable to a 

 laboratory worthy of the name, there is undoubtedly in many 

 quarters a lack of appreciation of systematic work, because it is 

 at the same time the most laborious and the most vexatious of 

 any form of biological investigation. It is becoming more and 

 more difficult every day to conduct systematic investigation away 

 from the special libraries indispensable to every well-equipped 

 laboratory, and unless a slight encouragement is given to the 

 laboratory student to take up some branch of systematic botany 

 this department of botanical science will be left largely in the 

 hands of the foreigner. 



One cannot emphasize too much the importance of a sound 

 knowledge of the geographical distribution of some of the more 

 lowly types of Cryptogams, particularly of the Desmidiaceae. 

 Such a knowledge, which can only be acquired by the patient 

 labours of the systematist, will throw much light on one of the 

 most interesting of all problems concerned with the later phases 

 of the earth's history, namely, the land-connections of previous 

 periods. 



The frontispiece consists of a reproduction of two photo- 

 micrographs to show some of the characters of the freshwater 

 plankton. One is a photograph of some material collected from 

 Loch Ruar, Sutherland, by Mr J. Murray, of the Scottish Lake 

 Survey (Pullar Trust). The other represents plankton of a 

 somewhat different nature from Lough Neagh, Ireland. 



G. S. WEST. 



ClRENCESTER, 



April 7th, 1904. 



