Function of Pyrenoids in Algæ

Abstract

THOUGH attempts have been made from time to time to explain the function of pyrenoids in Algæ, exact knowledge on the point is lacking. Usually starch is deposited around the pyrenoids in a good many Chlorophyceæ, and G. M. Smith¹ holds that pyrenoids synthesize starch. In starch–free diatoms G. Karsten² remarks that one has scarcely seen the actual formation of oils in connexion with pyrenoids. But by growing Rhopalodia gibba and Synedra affinis var. fasciculata in 2 per cent glucose medium, fatty acid and glycerine medium, etc., I could get distinct grouping of oil–drops around the pyrenoids (Fig. 1), the first–formed oil–drops in these diatoms being invariably deposited round the pyrenoids. Similarly, by growing green filaments of Spirogyra in fatty acids and glycerine medium, oil is synthesized in the course of three days in the form of drops (Fig. 2) around the pyrenoids within the starch–sheath. Chemical analysis confirms the utilization of acids in the process as the amounts of acids decreased during the process. Filaments of Spirogyra undergoing decomposition, either in Nature or in artificial culture, show the first formation of oil–drops around the pyrenoids within the starch-–heath as well as surrounding the sheath; here the starch–sheath becomes narrower and thinner—evidently oil is secondarily formed from the primarily formed starch–grains in the sheath.