OGlC/17 







,3: LIBRakY ^ 



MASS. Qv 



PREFACE 



This book deals A\'ith the principal groups of plants from the standpoint 

 of their structure, reproduction, and development. It presents a survey 

 of the plant kingdom Avith emphasis upon relationships as revealed by 

 basic similarity in bodil}' organization and life histories. It gives an 

 account of the general course of evolution that existing groups appear to 

 have followed. It endeavors to interpret, as far as possible, the struc- 

 tural and developmental complexities of the higher plants in terms of 

 the simpler conditions prevailing among the lower plants. 



The principal groups of plants are taken up in an ascending sequence 

 based on ever-increasing structural complexity. This order of pre- 

 sentation does not impl}^ direct phylogenetic relationship between 

 successive groups, even though in some cases such relationship may exist. 

 It merely denotes different degrees of progress from what is assumed to 

 have been a more primitive condition. Conclusions as to the derivation 

 of one group from another are based on substantial morphological 

 evidence, but are always tentative and subject to confirmation by 

 paleontological evidence. A true understanding of phylogeny can rest 

 onl\^ on the fossil record and, with a few notable exceptions, this is very 

 incomplete. 



The system of classification used as a basis for the presentation of the 

 principal plant groups is at once simple and conservative. The older 

 classification, which continues to be the one most widely used, has 

 certain limitations, but these arise mainly from uncertainties regarding 

 the affinities of many groups, particularly the lower ones. As long as 

 these uncertainties remain, there is little justification for abandoning an 

 established system of classification for a newer one. A somewhat simpli- 

 fied classification is adopted because of its greater convenience and 

 because more detailed schemes may be found in advanced works dealing 

 ^vith special plant groups. It is comprehensive enough to embrace, under 

 almost every class, the most important orders; but it generally does not 

 include families. 



Usually the outstanding features of each order are developed through 

 a detailed discussion of one or, more frequently, of several of its repre- 

 sentative genera. The distinguishing characters of the order are then 

 given in the form of a summar3^ Likewise the characters of each class 

 are summarized after all its members have been considered. These are 

 usually presented with the characters of related classes, so that a com- 



