83 



collections. The optimum temperatures plainly lie near the maxi- 

 mum, that is, about 80, and the season of growth approximates 

 that of the land flora, being limited to the months of April-Septem- 

 ber. This is a variable organism, and a number of species have been 

 described in the genus in recent years. Many of these" occur in our 

 waters, but no attempt has been made to separate them, since they 

 are based on minute characters. 



Mallomonas plosslii Perty. and M. producta Zach. These two 

 forms will be treated together, as in my opinion they are merely 

 divergent variants perhaps seasonal of a single species. In 1898 

 M. plosslii was found but three times in June and July and M. 

 producta eight times from May through September. In 1897 the 

 latter only was recorded, and in September and October. In 1896 

 M. plosslii appeared in July and M. producta in April and August. 

 In 1895 M. producta alone was recorded, and that in November. 

 The data are hardly sufficient for generalization, but so far as they 

 go they indicate that producta is more prevalent in late summer and 

 autumn and plosslii in early summer, the more attenuate form 

 (producta} in the warmer season. 



Biitschli ('80-' 89) has intimated that there may be some genetic 

 connection between Mallomonas and Synura uvella. Certain 

 features of its occurrence in our plankton lend their support to this 

 view. Synura in our waters is a winter planktont, with December 

 and February or March pulses. Mallomonas is a summer planktont, 

 making its first appearance during the time of the decline of Synura, 

 and when many of the colonies of the latter are breaking up into 

 their individual zooids. Again, the differences in structure and size 

 between the two genera are quite superficial, and might result from 

 the growth attending the free life of a Synura zooid and its prepara- 

 tion for sporulation. It is a noticeable phenomenon that the pro- 

 portion of sporulating individuals of Mallomonas in the plankton is 

 exceptionally large among all plankton organisms. "Free cells" 

 of Synura are plainly referable to that genus by their resemblance, 

 and by the fact that they are often united in clusters of several indi- 

 viduals forming fragments of disintegrating colonies. It may be 

 that some reproductive phase, as conjugation, intervenes between 

 the free-cell condition of Synura and the Mallomonas stage, and 

 that the relatively smaller numbers of the latter are due to the in- 

 frequency of this process. While the features of seasonal distribu- 



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