Some Alt/ff ()f Miunesotf.i Arthur. 101 



the floating iorni. aiul from Spirit L-ike, Iowa, with the fixed form, 

 to Geneva, N. Y., where it was intended to grow them in tanks 

 supplied with spring water, but all perished without giving any 

 results. 



The sudden appearance and disappearance of immense (jnan- 

 tities of these minute plants, by which large bodies of water are 

 filled with them and turned green within a few hours, is ascribed 

 by MM. Bornet and Flahault* in a recent paper on these phmts to 

 the action of sunlight. The jdants lying at the ])ottoui of the 

 water are started into active assimilation by strong light, which 

 ( auses bubbles of gas to be given oft' from the cells; this is held by 

 the gelatinous substance in which the filaments are iiubedded, and 

 when enough lias accumulated the balls are rendered sufficiently 

 light to float. When, in turn, the light becomes feeble, the gas 

 escapes, its }>roductiou stops, and the balls sink and disappear with 

 the same suddenness with which they came into view. 



More localities are now known for the alga' thjui at the time 

 of my first report. The writer noticed in 188P) that the water 

 fdants of East Okoboji lake in northeastern Iowa were thickly 

 ( overed with gelatinous masses. These were of various sizes up to 

 a foiirth of an inch in diameter, and often of irregular shape: 

 otherwise they resemble the attached form of the alga, mentioned 

 in the previous report. There were practically no free fioating 

 balls present. In June, 1884, however, the same locality yielded 

 ]ilenty of the floating form, which differed, in no appreciable way, 

 not even in size, from the Waterville plant. The floating form 

 was founi in August. 188-^, by Dr. Farlow, w^ith several other 

 members of the American Association, then in session at Minnea- 

 polis, in Lake Minnetonka, although not in large quantities. It 

 has also been reported as abundant in a lake in Minnesota (name 

 not given) in July. 1880, and published under the name Eicidar'xf 

 raijifins Thur., var. mlnutula Kirch.§ What is undoubtedly the 

 same species is reported from Iowa City, Eastern Iowa, under the 

 name Ghrotrichia Fisum Thur.f An alga on leaves of water 

 plants (Potaniof/eton) was found by liev. Francis Wolle.J at Beth- 

 lehem. Penn,, which may be the one under discussion, as it is 



*Bull. }*(>c. Bot. de France, \\\r, p. 80. 



fc; See Wolle, Bull. Torr. Bot. Club, vin, page 38. 



T Hobby. Proc. Io\A'a Acad. 8ci. 



+ Bull. Torr. Bot. Club, vi, page 138. 



