62 THE METABOLISM OF ALGAE 



products in cell division but is due to disorganization of 

 the leucoplast stroma while the cell remains capable of 

 growth and division. -^^ This disorganization has the appear- 

 ance of resulting from a gene-mutation.^'^' ^*^ 



Spontaneous apochlorosis has been noted only rarely, 

 but chlorophyll-less forms have been induced in Chlorella 

 vulgaris by irradiation with X-rays^^® and in Euglena 

 gracilis by treatment with streptomycin or by exposure to 

 high temperatures. 2'*^' ^^®' ^^^ Streptomycin appears to be 

 unique among antibiotic substances in exerting this effect. ^^^ 

 Streptomycin-induced apochlorosis, like that which occurs 

 spontaneously, results from disintegration of the chroma- 

 tophores. 



There exists in nature a large number of colourless and 

 therefore obligatorily chemotrophic forms which can readily 

 be recognized as related to pigmented algae because of simi- 

 larities in mdphology and in storage products. ^^^ These 

 forms have apparently been derived from pigmented species 

 by processes similar to those investigated in laboratory ex- 

 periments. Since streptomycin-producing actinomycetes are 

 common in soils it is possible that this substance may play 

 an important part in inducing apochlorosis in nature. The 

 pigmented species concerned are readily able to utilize 

 organic substrates so that colourless forms derived from 

 them would evidently stand a good chance of survival under 

 natural conditions. Only a few of the colourless algae that 

 have been described can be mentioned here. Species of the 

 genus Astasia are similar, except for the absence of pig- 

 ments, to species of Euglena. A. longa in fact, is identical 

 with a colourless strain of E. gracilis obtained in culture 

 experiments and has been renamed E. gracilis forma 

 hyalina.^^^ Polytoma spp. resemble Chlamydomoiias spp. 

 except in the matter of pigmentation and similarly Poly- 

 tomella corresponds to Tetrachloris.'^^^ Prototheca is evi- 

 dently a colourless Chlorella}'^ ^ ^^^ Colourless species have 

 been assigned to nearly every class of algae with unicellular 

 representatives (see refs. io6, 240, 243, 244). Besides those 

 obviously related to pigmented species there is a consider- 

 able number of forms which may have had an algal origin 



