CULTIVATING ALGAE — MEIEE 379 



It will be necessary to reinoculate subsequent agar plates before the 

 pure culture of the alga is obtained. Often a year's time and 

 endless patience are required before the pure culture is secured. 



By the monoculture method, a single cell is selected from a drop 

 of medium as it rests on the slide of the microscope. Kefined tech- 

 nique is necessary to operate the micromanipulator which removes 

 the cell and places it in sterile culture medium. 



The great majority of the forms isolated in pure culture are uni- 

 cellular green algae belonging to the Protococcales. Only a few mul- 

 ticellular or filamentous green algae, and some blue-green algae have 

 been successfully isolated so that they will grow on culture media 

 for any length of time. 



A number of modern workers have found pure cultures of algae 

 indispensable in their attempts to discover the effect of different min- 

 eral salts on the nutrition of the algae. The effect of light on algae 

 is steadily growing to be an important field of mvestigation. 



Chodat (1929), the Swiss algologist, with untiring zeal and bound- 

 less energy, has collected algae from the red snow at the summit of 

 the Alps to the basin of the Rhone. From cascades, pools, lakes, 

 and swamps, he has hunted the algae which form a part of his col- 

 lection of over 400 varieties of algae in pure culture. He has ably 

 demonstrated that m a population of algae that appear homogeneous 

 from a morphological point of view there are many physiological 

 and morphological races. Once selected, the descendants of a single 

 cell may maintain themselves unaltered and constant for a great num- 

 ber of generations. He emphasizes that the evolutionary cycle and 

 variation can not be studied in these forms without starting from 

 a single cell. 



Otto Warburg (1928), the German professor who was awarded the 

 Nobel Prize in medicine for 1931, utilized pure cultures of Chlorella 

 vulgaris and other closely related unicellular green algae for his work 

 on photosynthesis and cellular respiration. The study of normal 

 respiration can only be possible by avoiding any permanent injury to 

 the cells. The unicellular green algae lend themselves admirably to 

 this study as the mechanism of photosynthesis is complete in the tiny 

 unicellular individual with its green chloroplasts. The work would 

 be difficult and even impossible if not carried on in pure culture since 

 the presence of bacteria or other organisms might modify or stimu- 

 late the physiological processes within the algal cell. 



Robert Emerson (1929), an American student of Warburg, has 

 done noteworthy work on the function of chlorophyll in photosyn- 

 thesis in the algae. 



Van den Honert (1930), of Holland, used the filamentous alga 

 Hormidium in pure culture for intensive study of the assimilation 

 velocity of carbon dioxide. 



