CHAPTER X 



PHYSIOLOGY, SYMBIOSIS, AND SOIL ALGAE 



PHYSIOLOGY 



It would obviously be impossible to attempt a complete survey in 

 these pages of all that is known concerning the physiology of the 

 algae, especially as many species are very suitable objects for the 

 study of certain branches of physiology and in such cases a 

 voluminous literature has accumulated. Valonia has been fre- 

 quently used in experiments on absorption of solutes because of the 

 large size of the vesicles ; the Charales have been used in studies on 

 protoplasm because of the large size of their cells and the active 

 streaming of protoplasm that can be observed in forms such as 

 Nitella; Ulva, Hormidium and particularly Chlorella have been 

 repeatedly employed in experiments on assimilation; the eggs of 

 Fucus have also been objects of study from various points of view, 

 especially in reference to growth substances. In this chapter 

 certain recent papers have been selected for a survey because of 

 their more general interest and bearing on the life of the algae, but 

 their scope is by no means comprehensive and they have been 

 chosen in order to provide the student with some idea of the nature 

 of the knowledge that is being accumulated at present. The chapter 

 on Ecological Factors (cf. p. 349) will also be found to contain much 

 that can be regarded as algal physiology and should therefore be 

 consulted in this connexion. 



Chlorophyceae 



A recent study by Steward and Martin (1937) of the distribution 

 and physiology of Valonia at the Dry Tortugas in the West Indies 

 has brought out some interesting features. There are tsvo species 

 growing on the reefs that form the Tortugas ; V. macrophysa which 

 branches freely and V , ventricosa which is unbranched (cf. fig. 54)- 

 The former only grows in protected places, frequently where there 

 is no open communication with the sea, whilst the latter grows in 

 places exposed to the marine currents. The distribution of these 

 two species is therefore complementary and it is suggested that 



