26o 



THE ALGAE 



analogues which, so far as general 

 morphology is concerned, bear so much 

 resemblance to chlorophycean groups 

 that these forms are classed as Hetero- 

 chloridales, Heterococcales, Hetero- 

 siphonales and Heterotrichales. 



Heterochloridaceae : Chloramoeba 

 (chlor, green; amoeba, changing). 

 Fig. 147 



This is a naked unicell which is 

 analogous to certain members of the 

 Volvocales, e.g. Dunaliella. The cells 

 multiply by longitudinal division, but 

 under adverse conditions eUipsoidal 

 cysts with large oil globules are de- 

 veloped and these form a resting 

 stage. 



Fig. 147 A, Chloramoeba 

 heteromorphai cyst. B, the 

 same, motile phase, c = chloro- 

 plast, n= nucleus, z;= vac- 

 uole. Cj flagellum structure 

 in Monocilia. (After Fritsch.) 



Heterocapsaceae : Botryococcus (botryo, cluster; coccus, berry). 

 Fig. 148 



This fresh-water genus represents one of the palmelloid ana- 

 logues of the Chlorophyceae, the principal species, B. braunii, 

 forming an oily scum on ponds and lakes in spring and autumn, 

 whilst in late simimer the cells are often coloured red by haemato- 

 chrome. The colonies vary greatly in shape, the cells being radially 

 arranged into spherical aggregates that are connected in a reticular 

 fashion by tough, hyahne or orange-coloured strands belonging to 

 the lamellated mucous envelope. The thin cell wall is said to con- 

 sist of two unequal pieces, but despite this xanthophycean feature 

 the alga is anomalous in that starch is said to be formed. The indi- 

 vidual cells are surrounded by a thin membrane that becomes 

 evident when they are squeezed out of their envelopes as some- 

 times happens. Each cell is enclosed in a fimnel-shaped mucilage 

 cup composed of several layers and prolonged at the base into a 

 thick stalk. In old colonies the mucilage envelope swells up so that 

 the cup structure is obscured, but although the sheath is so pre- 

 dominant nevertheless its origin is not clearly known. The cells 

 multiply by longitudinal division, whilst asexual reproduction by 

 means of zoospores has also been recorded though it requires con- 



