87 



Chlorella vulgaris). These experiments produced negative results at 

 first, but in a footnote and in a postscript BEIJERINCK communicates 

 that he succeeded in the isolation of the Hydra-alga., and that he 

 could identify it as Chlorella vulgaris. 



The isolation of the gonidia of Physcia parietina, which he designated 

 with BORNET as Cystococcus humicola Nageli (later on, with WILLE, 

 as Chlorococcum humicola}, was easier, and this alga also appeared 

 to thrive only satisfactorily on nutrient-media containing peptone. 

 This led BEIJERINCK to call the Lichens "Doppelparasiten" ; the 

 colourless component should profit from the carbon dioxide assimila- 

 tion of the green symbiont, and the latter from the protein synthesis 

 of the colourless fungus. 



In 1893 BEIJERINCK gave a short report on the status of his pure 

 cultures of "niederen Algen" '), and in 1898 he communicated that he 

 had finally succeeded in preparing a pure culture of Pleurococcus 

 vulgaris, which occurs very widely on the trunks of trees, roofs, and 

 walls 2 ). The isolation of PI. vulgaris appeared possible, however, only 

 on an agar plate which has been \vashed out and freed from all soluble 

 organic matter, and then provided with inorganic salts. Most re- 

 markably, BEIJERINCK was able to ascertain that this organism can 

 adapt itself to organic nutrition. 



A publication of 1904 3 ) deals with an alga which BEIJERINCK isola- 

 ted from "Ulmenfluss", and which he designated as Chlorella variegata 

 since the colonies of pure cultures show, next to distinctly green parts, 

 also lighter coloured parts formed by cells which possess less chloro- 

 phyll. 



Further very interesting illustrated communications on this species 

 of the Family of the Protococcoideae are to be found in the classical 

 treatise entitled "Mutation bei Mikroben" 4 ), which dates from 1912. 

 It is shown therein that Chi. variegata produces two mutants, one of 

 which occurs very regularly on nutrition media containing organic 

 matter. This mutant, designated as Chlorella variegata aurea, is 

 characterized by incomplete formation of chlorophyll in the chloro- 

 plast. More rarely in cultures, but presumably regularly in nature, a 

 second mutant occurs which BEIJERINCK called Prototheca Krilgeri, 

 which has completely lost the power to make chlorophyll (not, how- 

 ever, that of forming glycogen in the chloroplast which has become 

 colourless, and which BEIJERINCK designates as "glycophor"). BEIJE- 

 RINCK feels here that he is justified in assuming a transition from an 

 alga into a fungus, and he states that therewith "die zuerst von SACHS 



') Bericht iiber meine Kulturen niederer Algen auf Nahrgelatine, Centralbatt fur 

 Bakteriologie und Parasitenkunde 13, 368-373, 1893 (}'e>-(tniehlt' Geschriften 3, 21- 

 25). 



2 ) Notiz iiber Pleurococcus vulgaris, Centralblatt fiir Bakteriologie und Parasiten- 

 kunde II. Abt, 4, 785-787, 1898 (Vevzamelde Geschriften 3, 293-295). 



3 ) Chlorella variegata, ein bunter Mikrobe, Recueil travaux botaniques norrl. 

 1, 14-27, 1904 (Verzamelde Geschriften 4, 231-238). 



4 ) Folia Microbiologica 1, 1-97, '1912 (Verzamelde Geschnftcu 5, 25-1 



