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 by 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) 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 (1889) to which the genus 
Ruppia belongs, comprise an interesting family 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. 
