410 



Heterococcales 



many times longer than their diameter and almost always curved, in very 

 many cases being spirally contorted (fig. 261 A). There is, as a rule, 

 a distinct base and apex to each cell, the base being produced into a stalk or 

 a short spine and the apex more or less distinctly swollen (fig. 201 A). 

 Sometimes both ends of the cell are similar, either blunt or spined (fig. 261 H 

 and /). There is at first a single nucleus, but in the larger and more 

 elongate cells several nuclei have been detected. The chromatophores are 



rather large, parietal and (in optical 

 section) H -shaped, being arranged 

 in a series from end to end of the 

 cell. Pyrenoids do not occur, but 

 in some species oil-globules are a 

 conspicuous feature of the cells. No 

 vegetative division occurs and re- 

 production so far as is definitely 

 known is entirely asexual. It takes 

 place normally by the division of 

 the protoplast to form ellipsoidal 

 aplanospores (up to 16 in number), 

 which escape from the apical end 

 of the mother-cell by the detach- 

 ment of a lid. More rarely zoogonidia 

 are produced, 8 in each cell, and 

 these also escape from the apex of 

 the cell. The existence of gametes 

 has been suspected, but is doubtful. 

 In the attached forms, which were 

 at one time placed in the genus 

 Sciadium, the zoogonidia usually come to rest on the rim of the empty 

 tube-like mother-cell and there grow into a colony of adult cells. Another 

 generation may be formed in a like manner from each of these cells and thus 

 a curious umbellate colony may be built up. 



The structure of the cell-wall was carefully investigated by Bohlin ('97), 

 who found that it was essentially similar to that exhibited by Tribonema 

 (vide fig. 262). 



In Bumilleriopsis brevis (Gerneck) Printz the cells are comparatively short, 

 bent, and irregularly cylindrical, with parietal discoidal chromatophores. 

 Moreover, the cell never has more than one nucleus. 



The genera are : Ophiocytium Nageli, 1849 [inclus. Sciadium A. Br., 1855] and 

 Bumilleriopsis Printz, 1914. Species of Ophiocytium are common in both temperate and 

 tropical countries, very often occurring in small ponds and pools in which there is 

 a deficiency of aeration. 



Fig. 261. A, Ophiocytium majits Nag. B G, 

 aplanospore-formation and germination of 

 aplanospores in O. cochleare (Eichw.) A. Br. 

 II and I, 0. bieuspidatum (Borge) Lemm. forma 

 longispina Lemm. J, 0. Arbuscula (A. Br.) 

 Rabenh. K, 0. graciliceps (A. Br.) Babeuh., 

 after treatment with potassium hydrate. A J, 

 x 450 ; K, x 570 (after Bohlin). 



