INTRODUCTION 



Of late years there has been manifested a tendency toward a 

 systematic investigation of the internal structure of plant species, 

 as contrasted with the more superficial description of external 

 characters by systematists. For although, as stated b\' Campbell 

 (1897), a description of external characters "is usually quite suffic- 

 ient for the mere identification of a plant, and for determining its 

 relation to nearly allied forms, it is quite inadequate for settling 

 questions of relationship between more remote groups, and espec- 

 ially those of obscure affinities." 



This movement has been directed especially to the study of the 

 origin and development of the sexual generation in Spermatophytes 

 and the problems of embryology in this group, resulting in an over- 

 whelming mass of literature on these subjects. 



But, in the meantime, it is commendable that some botanists have 

 also directed their attention to a study of the internal structure of 

 the vegetative organs : for it is only by a complete account of the 

 development and structure of the whole plant, together with its 

 life history, that we can hope to acquire sufficient knowledge for 

 the solution of one of the most interesting and vitally important 

 problems in all plant morphology — i. e., the interrelationship of the 

 various plant groups. 



Some of the recent works of Campbell ^1897, 1898 1 are most 

 noteworthy in presenting in this way a connected account of several 

 species, especially certain little understood monocotyledons. 



The present work, extending over a period of five years, was 

 undertaken with a similar purpose : and seeks to comprehend, as 

 far as possible, a connected account of the development and structure 

 of the plant organs, together with the life history, of one of the 

 simpler monocotyledons. Ruppia maritima. 



The Potamogetonaceae of Ascherson ('1889j to which the genus 

 Ruppia belongs, comprise an interesting famih' of remarkably simple 

 plants. As to whether this simple structure represents a primitive 

 or a reduced condition is an extremely important question, but in 

 the present state of our knowledge a clear, unassailable verdict on 

 either side is impossible. A discussion of this point will, however, 

 be postponed for the present. 



