90 G. F. PAPENFUSS 



well the usefulness of cultures in the study of questions which as 

 yet have received very little attention. 



Schreiber (1935) succeeded in culturing plants of Dictyota 

 dichotoma (Huds.) Lamour. which in stature approached those 

 occurring in nature. Branches that are removed from the plants 

 regenerate complete thalli and thus make it possible to obtain 

 may individuals of identical genetic constitution. Schreiber also 

 succeeded, in a number of instances, in raising to sexual maturity 

 the four plants developing from a tetrad of spores in Dictyota, 

 and found that invariably two of them were male and two female 

 individuals, which proved conclusively that sex was determined 

 genotypically. 



From this work it is apparent that Dictyota offers immense 

 possibilities (as perhaps do related genera) for the study of gen- 

 etic problems in the brown algae. 



Schreiber (1930) has also demonstated experimentally that in 

 Laminaria saccharina (L.) Lamour. sex determination is geno- 

 typic. Furthermore, he found that the eggs of some species of 

 Laminaria will develop parthenogenetically. The resulting sporo- 

 phytes grew well but were atypical. Whether or not they were 

 capable of producing reproductive organs was not determined. 

 Experiments designed to determine if related species would hy- 

 bridize gave negative results. No cross fertilizations occurred. 

 Schreiber expresses the opinion that an algal genus such as ham- 

 inaria probably represents a much more comprehensive entity 

 than a genus such as Cirsium in the Compositae and phylogenet- 

 ically perhaps is the equivalent of the entire family Compositae. 

 Although Schreiber's failure to obtain cross fertilization in ham- 

 inaria does not justify such a sweeping statement, it does empha- 

 size the need for many more studies of this kind in the algae. 



Rhodophyta® 



Although a considerable amount of work has been done on 

 the development in culture of the sporeling stages of red algae 

 (Killian, 1914; Kylin, 1917; Chemin, 1937; Inoh, 1948; and many 



^ See footnote, p. 79. 



