HOW TO KNOW THE SEAWEEDS 



It will be worth while for the student to take particular notice of 

 the apices of branches in the Red Algae, for in that group especially 

 the characteristics of the apex will provide important clues for identi- 

 fication. He will find, for example, that the presence of a single apical 

 cell is usually associated with the presence of a central axial filament 

 and that the recognition of these and of other such features may be 

 important in understanding the vegetative structure for the purpose of 

 interpreting correctly the steps in the key. 



It will become evident as experience is gained in making cross 

 sections for the purpose of reveaUng the features of internal structure 

 that young portions of a plant are much more satisfactory for section- 

 ing than very old ones. The additional complications contributed by 

 secondary growth of certain tissues often obscure the important basic 

 features of structure. Accordingly, one should exercise some care in 

 the selection of a suitable fragment for sectioning, or should repeat the 

 operation on several different parts if difficulties are encountered in 

 the first interpretation. 



The manner of attachment to the substrate differs widely in the 

 marine algae, from a holdfast consisting of a single modified basal 

 cell, to various kinds of penetrating or entangling rhizoids, multicel- 

 lular, adherent discs, creeping stolons, and massive clasping hapteres 

 (Fig. 8). In many instances the kind of attachment constitutes an im- 

 portant generic or specific character, and identification may be im- 

 possible without a knowledge of it. Accordingly, it is important for 

 the collector to obtain complete plants including the holdfast wherever 

 possible, even if this may require breaking the rock upon which a 

 specimen is growing. 



REPRODUCTIVE STRUCTURES 



NLIKE the several seed-bearing marine flowering plants 

 which are treated at the end of this book, the algae re- 

 produce, with few exceptions, by means of microsco- 

 pic spores. Although these spores themselves are very 

 small, the reproductive structures which produce them 

 are often large enough to be visible to the unaided 

 eye and are useful in providing distinctive characters for classifica- 

 tion purposes. For this reason the student should acquaint himself with 

 some of the more general aspects of algal reproduction before endeav- 

 oring to identify his specimens. 



The widespread misconception that the algae are "just simple, 

 primitive plants" is quickly di-spelled when one studies their marvel- 



19 



