CULTURE AND MORPHOLOGY 79' 



the composition of sea water may be obtained from the works of 

 Schiller (1928), Sverdrup, Johnson and Fleming (1942) and Lev- 

 ring (1946). 



Chlorophyta'^ 



Since 1925, when Miss Williams showed that Codium was a 

 diploid alga, our concepts of the life cycles of green algae, espe- 

 cially the marine forms, and of the associated nuclear phenomena 

 have undergone a profound change. It is now known that the 

 Siphonales and Dasycladales are diploid algae, or at least those for 

 which the cytology has been studied, and that it is the diploid soma 

 which in them, as in the Fucales and in animals, functions as the 

 gamete-producing generation. In certain other orders, such as the 

 Cladophorales (Cladophora, Chaetomorpha), Ulvales (Ulva, En- 

 teromorpha) , Ulotrichales (Draparnaldiopsis, Fritschiella; Singh, 

 1945 and 1947, respectively) and Siphonocladales {Anadyomene, 

 Microdictyon; Iyengar and Ramanathan, 1940 and 1941, respec- 

 tively) there are forms the life cycle of which includes an alterna- 

 tion of isomorphic generations; and Juller (1937) has shown that 

 Stigeodonium subspinosum Kiitz. (Ulotrichales) possesses an al- 

 ternation of heteromorphic generations, with the diploid, asexual 

 generation smaller than the haploid one. 



Although the green algae have not been cultured as exten- 

 sively as would be expected, there are many advantages in this 

 method of approach in the study of problems in this group, as 

 may be gadiered from the following brief review of some of the 

 work that has been done. 



Following the discovery of an alternation of isomorphic gen- 

 erations in the life cycle of members of the orders Cladophorales 

 and Ulvales by Hartmann (1929) and F0yn (1929, 1934, 1934a), 

 several genera and a variety of species of these two orders have 

 been found to possess a similar cycle. However, it has also been 

 shown, that there are forms which deviate from this seemingly 

 general rule. Through a long series of papers Eliding (1948, 

 1948a, and earlier) has tremendously advanced our knowledge of 

 the life cycle and taxonomy of species of the genus Entero- 



^See Papenfuss (1946) on nomenclature for the phyla of algae. 



