406 BULLETIN OF THE BUREAU OF FISHERIES. 



PART II. SYSTEMATIC ACCOUNT OF THE ALGiE. 

 IDENTIFICATION OF ALG/E. 



The main groups of algae are usually easily distinguished, since they differ markedly 

 in their structure and usually in their color. 



The Myxophyceae, or "blue-green algae," consist of cells of relatively simple struc- 

 ture living singly or joined into loose colonies or united into filaments; they are usually 

 gelatinous and, as their common name implies, usually have a dark, blue-green color. 

 By these characters they are easily distinguished from all others. 



The Chlorophyceae, or "green algae," consist of single cells, filaments, sheets, or 

 more complex structures. If the structures are complex, they are not composed of 

 closely packed cells, but of interwoven filaments which are easily seen when teased apart 

 and examined with slight magnification. They are light or dark yellow green, the color 

 of grass and leaves, and are not likely to be mistaken for any other group. Some of them 

 are encrusted with lime. 



The Phaepphyceae, or "brown algae," are easily distinguished by their brown color, 

 which may, however, have the shade of walnut or mahogany, or may tend toward olive 

 green. They consist of filaments or of more or less complex cellular structures. 



The Rhodophyceae, or "red algae," consist of filaments, sheets, irregular aggre- 

 gations, or complex cellular structures of various forms. They sometimes furnish diffi- 

 culties to beginners, since their color and form are extremely various, the former ranging 

 from red or pink to dark purple on the one side and to a decided green on the other. If 

 green, they may be distinguished by the fact that their structure, at least in part, shows 

 a close cellular arrangement and does not consist entirely of interwoven filaments. A 

 still surer character for fertile specimens, once it has been recognized, is the fruit borne 

 by all but the simplest members of this group. This is the cystocarp, which consists 

 essentially of a mass of spores radiating from a common center and surrounded by a 

 sterile jacket of some sort. This may be immersed and relatively inconspicuous but 

 frequently forms more or less conspicuous conical projections above the surface. Even 

 when immersed it is usually plainly seen as it is borne in a swollen part of the frond. 



While, however, the main divisions are easily distinguished, the smaller groups 

 often furnish considerable difficulty. Once they have been seen, the genera of the blue- 

 green, green, and brown algae may usually be easily recognized, or may even be identified 

 with certainty from illustrations, but it is often difficult to place a given specimen of red 

 algae in its proper genus or even in its proper family or order. In many cases species 

 of all the divisions are distinguished with great difficulty and only after careful study 

 and comparison of many specimens. It can not be hoped, therefore, that the following 

 descriptions will enable a determination to be made in every case. It should be borne 

 in mind by a beginner that, while many forms may be recognized at a glance, others 

 require much study and can be determined only when all the distinguishing characters 

 are present. Frequently forms must be left undetermined because the material is not 

 sufficient. One should, therefore, collect an abundance of every unknown species. In 

 all cases it is desirable to compare the specimens with some that have been correctly 

 determined, since one good specimen will convey a better idea of the species than it is 

 possible to get from pages of description. Those using the keys given here should 

 remember that these are made only for the species that have been found in this region, 

 and if used in other regions or if other species should be found here, they may 

 lead the beginner astray. 



