Introduction 



Although convenient, the term algae has been applied to such a 

 great variety of plant groups and has been given so many interpreta- 

 tions that it has no very precise meaning. In the broadest sense it 

 may refer to all chlorophyll-bearing thallophytes and protista, and 

 their colorless close relatives. Life history studies have established 

 genetic relationships between definitely plant-like and animal-like 

 algae. Thus the incorporation of the Volvocales in the phylogeny of 

 the Chlorophyta is necessary. Other protozoa-like, pigmented 

 organisms, such as the Euglenophyta and the Cryptophyceae and 

 other Pyrrhophyta, are examples of evolutionary lines which appar- 

 ently have ended blindly in their present expressions. One might 

 contend, therefore, that their inclusion among the other definitely 

 plant-like algae cannot be justified because, unlike the Volvocales, 

 they have no phylogenetic connections with the group. Notwith- 

 standing the fact that the Euglenophyta and Pyrrhophyta include 

 some colorless and definitely protozoa-like relatives, the groups merit 

 a place in phycological study by virtue of their many plant-like at- 

 tributes. Likewise, chlorophyll-bearing, bacteria-like organisms must 

 be given a place in the broad definition of the Cyanophyta. Many of 

 the organisms belonging to the Chrysophyta have only a few char- 

 acteristics which entitle them to a place among the algae, but be- 

 cause the morphology and the habits of some members are funda- 

 mentally plant-like their inclusion is clearly justified. 



Whatever limits of classification may be set up for the algae, all 

 these groups of simple organisms are interesting to the phycologist, 

 the aquatic biologist, the limnologist, and the oceanographer. In 

 order to meet a number of these interests and to make the present 

 work as useful as possible, the broader interpretation of the algae 

 has been adopted and representatives from the eight divisions are 

 treated here. ( There are eight divisions, or phyla, if one recognizes 

 the Chloromonadineae. This little-known class is represented by 

 Gonyostomum semen Dies, in our collections.) Hardly any two phy- 

 cologists are in complete agreement on the disposition of forms with- 

 in the algal groups. The taxonomist will note, therefore, many 

 inconsistencies if the details of the arrangement used here are com- 

 pared with any one of the several schemes followed in handbooks, 



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