194 



Tetrasporinese 



not in accord with our present knowledge of the inter- relationships of the 



Protococcales. 



The other important genus of the Protococcacese is Chlorella (fig. 120), 

 which differs from Pr.otococcus chiefly in the thin- 

 ness of its cell-wall. Several distinct species are 

 widely distributed, occurring on damp ground, on 

 bark, and also in purely aquatic habitats. One 

 of the most generally distributed is Chlorella 

 vulgaris (fig. 120.4 C) which occurs in stagnant 

 water, and is also found in symbiotic relationship 

 with various Infusoria such as Param&cium,- 

 Ophrydium, Stentor, etc.; and also in Hydra 

 viridis. These symbiotic forms are known in a 

 general way as ' zoochlorellse.' Chlorella vulgaris 

 often appears in quantity in impure cultures of 

 Algae and has been itself the subject of much 

 experimental work by Artari ('92), Grintzesco 

 ('03) and others. The chloroplast is parietal, bell- 

 shaped or reticulated, and with or without a 



Fig. 120. A C, Chlorella vul- py reno i(l. Reproduction occurs by the successive 



gans Beijer. ; A, vegetative r>7 



cell ; B and C, stages in divi- bipartition of the original protoplast, the daughter- 



jDandE ?W faginea ?Gerneck) ce ^ s ra pidly developing a delicate cell-wall and 



Wille, x520 (after Gerneck). remaining quite free within the mother-cell. 

 F I, Chi. miniata (Kiitz.) f \ i . -^u iv 11 



Wille (=Paimcilococcus mini- The wall of the latter either splits open or swells 



cell*- ^^^'.^j^?^* 1 ^ up and becomes diffluent, thus setting free the 

 and I, formation and escape daughter-cells. In both Trochiscia and Chlorella 

 the formation of the daughter-cells is almost 

 exactly like the formation of zoogonidia in so 

 many of the Protococcales, and it is not unlikely that they are reduced 

 zoogonidia. Many of the recently described 'genera' of unicells found in 

 cultures are referable to Chlorella. 



The genera are : Protococcus Agardh, 1824 [inclus. Pleurococcus auct. but possibly not 

 of Meneghini, 1842; ^.Diplosiphon Bialosuknia, 1909]; Trochiscia Kiitzing, 1845 [ = Acan- 

 thococcus Lagerheim, 1883] ; Entophysa Mobius, 1889 ; Chlorella Beijerinck, 1890 [inclus. 

 Protococcus auct. ; Palmellococcus Chodat, 1894 ; Chloro'idium Nadson, 1906 ; Krugeria 

 Heering, 1906; Planophila Gerneck, 1907; Chlorotetras Gerneck, 1907; Acrospk&ria 

 Gerneck, 1907 ; Chlorosarcina Gerneck, 1907]. 



Chlorella miniata (Kiitz.) Wille is a frequent Alga in greenhouses, forming a soft 

 brownish-green stratum, which often turns orange-red, on the outer surfaces of moist 

 plant-pots, etc. Numerous ' species ' of Chlorella have recently been described, mostly on 

 cultural characters (vide Chodat, '09 and '13). An elaborate physiological investigation of 

 Chlorella luteo-viridis var. lutescens Chodat has recently been made by Kufferath ('13). 



It is quite possible that the Algae described by Klebs ('83) and others as species of 



