USE OF THE PICTURED-KEY 



HE success with which the following key may be used 

 will depend firstly, upon the adequacy of the speci- 

 mens for identification, secondly, upon the care with 

 which they are examined, and thirdly, upon the ac- 

 curacy with which terms in the key are interpreted. A 

 microscope is a prerequisite in this study, for many of the marine algae 

 can be identified only by observing certain features of reproduction or 

 of internal anatomy. However, in the present key an attempt has been 

 made to simplify the identification process so that, for the most part, 

 only relatively gross microscopical examinations are required. In- 

 deed, the student will find that a number of the larger algae, espe- 

 cially those bearing vesicles, veins or ribs, may be identified en- 

 tirely on macroscopic characters. 



It cannot be overemphasized that the specimen must be adequate 

 before identification is attempted, for a juvenile, sterile, or fragmentary 

 algal specimen will often present the same difficulties with respect 

 to the use of a key as does a flowering plant for which only a leaf 

 or a piece of root has been collected. As more and more field ex- 

 perience is gained by the student, the problems of recognizing and 

 selecting suitable specimens will diminish. 



The key treats of marine algae such as may be encountered on 

 any coast of the continental United States, and it will be noted that 

 in a good many instances a genus will occur on both Atlantic and 

 Pacific coasts. However, a rather large proportion of the algae ore 

 relatively localized, and for this reason an indication of the geographic 

 distribution is given in each case. 



Of necessity, for lack of space, only the larger and commoner 

 marine algae are treated here, and in the majority of cases only as 

 to genus, although the full specific name is provided for most of the 

 habit illustrations. Thus, the student must be aware that some of the 

 genera of plants he collects in any given area may not be illustrated 

 in this brief account. 



It should be pointed out here that the sequence in which the genera 

 appear in the key is entirely artificial and bears no necessary con- 

 nection with phylogenetic relationships. However, in order that the 

 student may orient himself as to the relationships of the various plants, 

 each is numbered in the index according to an appended list in which 

 they appear in the phylogenetic sequence ordinarily encountered in 

 the more modern taxonomic treatises. 



26 



