gO WISCONSIN PHYTOPLANKTON 



CHLOROCHROMONAS Lewis 1913. 



Cells solitary, generally free-swimming, very rarely amoeboid, some- 

 times attached to substratum by a posterior pseudopodia-like structure. 

 Cell shape pyriform to sub-ovoid, with an oblique depression at the 

 anterior end. Cilia two, at the anterior end of the cell and of unequal 

 length. Chromatophores two, yellowish-green in color, oblong with 

 rounded ends in front view, somewhat flattened in side view. Cells 

 with a single anterior vacuole, one nucleus, and without an eyespot. 

 Nutrition holophytic or saprophytic. 



Reproduction by longitudinal fission when in the motile phase. 



CHLOROCHROMONAS MINUTA Lewis. PI. 15, Figs. 1-3. 

 Arch. f. Protistenkunde 32: 254, pi. 12, figs. 1-24. 1913. 



Characters as described above. (Euplanktont). 

 Cells 4.5-9.5 (av. 6.3) p, long, with an average breadth of 4.7 p.. 

 Average length of longer cilium 12.5 //,, of the shorter 2.9 /JL. 



Mendota. 



This organism was first found by Lewis in a dish containing sections 

 of basswood (THia americana) that had been standing for some time in 

 a dish of tap water, which is drawn directly from Lake Mendota. I 

 have never noted the alga in plankton collections but have no doubt 

 but that a continued search will demonstrate its presence in Lake Men- 

 dota. During the past winter (1917-18) the alga appeared in an in- 

 fusion of fern leaves which had been standing for some time in tap 

 water. This shows that the original source of the alga was the water 

 with which the sections were moistened and not the Tilia. 



Order HETEROCOCCALES. 



Cells spherical, ovoid, saccate, or elongate cylindrical ; solitary or in 

 colonies of definite or indefinite shape; free-floating or sessile. Cells 

 of colonies embedded in a hyaline, gelatinous envelope or a tough elastic 

 membrane. Chromatophores one to many, yellowish-green to nearly 

 grass- green in color and with oil not starch the assimilation product. 



Asexual reproduction by vegetative cell division and a formation of 

 zoospores with cilia of unequal length. 



Sexual reproduction by a fusion of zoogametes that are similar in 

 structure to the zoospores is known in certain genera. 



