Induced Periodicity of Photosynthesis and Respira- 

 tion in Hydrodictyon 



A. PIRSON, Botanisches Institute, Universitnt Marburg, Marburg/Lahn, 



Germany 



The comparison of highly organized algal cells with cells of the 

 simple unicellular green algae as standard ol)jects of photosynthetic 

 research led us to investigations of photosynthesis and aerobic res- 

 piration of Hydrodictyon, which, by previous examinations in our 

 laboratory (]), proved to be suitable for simultaneous measurements 

 of morphological, cell-physiological, and metabolic properties. 



Hydrodictyon forms netlike colonies; the meshes of the loose net- 

 work are formed by single cells. Growth of these colonies does not 

 occur by cell division, but entirely by an easily determinable elonga- 

 tion of the cells, in the course of which the cells change over from the 

 young mononuclear stage into a multinuclear one. The chloroplast 

 forms are more or less perforated hollow cylinders. After the cells 

 have reached a certain length, the numerous nuclei of each cell can 

 be caused by simple methods, e.g., temporary treatment with strong 

 light, to form zoospores together with a small portion of cytoplasm 

 and plastid material. Normally these zoospores are not freed but 

 unite after a short time within the mother cell, forming a daughter 

 net, which, after a rapid disintegration of the mother membrane, 

 is liberated and then starts the vegetative cycle again. The numerous 

 cells of a net yield quite a homogeneous material with but little 

 physiological deviation. Besides the vegetative cycle, Hydrodictyon 

 also exhibits a sexual cycle, which, however, can be completely elimi- 

 nated by suitable culturing conditions. In any case, growing this alga 

 requires more supervision than does culturing algae of the Chlorella 

 type. As the concentration of the nutrient medium (solution of 

 Uspenski) must be kept low, a frequent change of solution is neces- 

 sary in order to avoid mineral deficiencies. 



Among the physiological c;omplications brought about by the 

 higher morphological differentiation it is particularly remarkable 

 that Hydrodictyon, in contrast to Chlorella, requires a regular al- 

 ternation of light (400 to 800 lux) and darkness for its normal develop- 



490 



