Coelastrum sphaericum Naegeli 1849, p. 98 



PI. 53, Fig. 7 



Coenobium ovoid, composed of conical cells, the narrow end 



directed outward, adjoined without processes along the lower lateral 



walls, forming interstices which are equal to or greater than the 



diameter of the cells; cells up to 25/x in diameter. 



Euplankter. Mich., Wis. 



FAMILY BOTRYOCOCCACEAE 



This family is composed of plants which have ovoid or spherical 

 cells embedded and crowded in tough, often foamy, irregularly 

 shaped masses of mucilage which are frequently darkly colored and 

 semi-opaque. In some species the cells are inclosed in a cup of fatty 

 substance with an outer layer of pectic material. The chloroplast is 

 an open or close parietal net-work, usually with 1 pyrenoid. Both 

 starch and oil accumulate as food reserve, the latter often so dense 

 as to obscure the true nature of the cell content. Asexual reproduc- 

 tion is carried on by autospores. 



As here defined, this family includes only the genus Botryococcus 

 which has been given various taxonomic positions. Because the fatty 

 material in which the cells are embedded is so darkly colored in the 

 type species, B. Braunii Kuetz., the exact nature of the cell content 

 and pigmentation has been difficult to determine. Until recently the 

 genus has been placed in the Heterokontae ( Chrysophyta ) with a 

 few other genera, to comprise the family Botryococcaceae. The 

 critical studies of Blackburn (1936) on Botryococcus Braunii Kuetz., 

 however, seem to establish the identity of this species as a member of 

 the Chlorophyta. The morphology of the wall, the presence of 

 a pyrenoid and of starch, and the habit of retaining mother cell 

 membranes and secretions in the building of the colony justify the 

 removal of the genus from the Chrysophyta. Blackburn ( I.e. ) rightly 

 proposes that the Botryococcaceae be placed near the Dictyo- 

 sphaeraceae. See page 237. 



BOTRYOCOCCUS Kuetzing 1849, p. 892 

 [Ineffigiatus West & West] 

 Thallus an irregularly globose or buUate colony of ovoid or 

 spherical cells densely arranged somewhat radially in a sticky, often 

 dark-colored mucilage, the cells embedded in a cup-like sheath of 

 fatty material in one species; compound or net-like aggregates of 

 colonies may be formed by long or short strands of rubbery mucilage 

 connecting several clusters of cells; chloroplast a fine or close 



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