Systematic Account 



Structural terms are illustrated in the preceding section and are 

 defined, together with other technical terms, in the Glossary. 



DIVISION CHLOROPHYTA 



Plants belonging to this group are characterized by grass-green 

 chloroplasts, one to many in each cell or protoplasmic unit. In most 

 forms the chloroplast contains one or more pyrenoids, which ac- 

 cumulate starch as a food reserve. Even in plants which do not pos- 

 sess a pyrenoid, presence of starch makes possible the use of the 

 iodine test for separating doubtful forms from those Chrysophyta 

 which are similar in general appearance. 



The cell wall, which is firm in most genera, is composed of cellu- 

 lose and pectic compounds. There may be, also, a mucilaginous outer 

 layer. 



See G. M. Smith (1933, 1938) and F. E. Fritsch (1935) for a 

 discussion of the reproduction and the taxonomy of this division; 

 Collins (1909, 1918, 1918a) on the taxonomy; Blackman (1900), 

 Blackman and Tansley (1902), and Fritsch (1916) on the phylogeny. 

 The modern interpretation of this division recognizes two classes, 

 Chlorophyceae and Charophyceae. 



CLASS CHLOROPHYCEAE 



This class, commonly known as the green algae, includes a great 

 variety of forms: unicells (sometimes motile), simple or well- 

 organized colonies, simple or branched filaments, partitioned coeno- 

 cytes, and true coenocytes ( filaments without cross walls ) . The chief 

 evolutionary series in the Chlorophyceae begins with the motile uni- 

 cells of the Volvocales. 



The methods of reproduction, both asexual and sexual, vary 

 greatly within the several orders. In some orders, the sexual repro- 

 ductive methods and organs are unique and serve as a basis for 

 classification. This is particularly true for the Zygnematales (Con- 

 jugales), the Oedogoniales, and the Siphonales. 



See the authors mentioned above, as well as Oltmanns (1922), for 

 an account of reproduction and life histories in the Chlorophyceae. 



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