254 FIRST FORMS OF VEGETATION. 
different Rivularias, affect running water ; others 
are found only in wells, such as the beautiful and 
delicate Draparnaldias ; and others are partial to 
lakes, such as the Chetophoras. The Irish lake 
of Glaslough is remarkable for its greenness 
occasioned by Oscéllatoria eruginosa. Ulva ther- 
malts lives in the hot springs of Gastein, the 
temperature of which is 117° Fahr. Calothrix 
nivea luxuriates in the sulphuretted hydrogen 
water of Harrogate. Protococcus salinus gives 
a crimson colour to salt-water tanks on the 
coast of the Mediterranean. Hematococcus Nolti 
reddens the marshes of Sleswick-Holstein. Bally- 
drain lake in Ireland is coloured a lovely green 
by Anabaina spiralis. The fruiting season of 
the fresh-water alge is in spring and early 
summer. They rise then from the bottom of 
the water, where they lay all winter unseen ; and 
buoyed up by the globules of gas which they 
eliminate, and which gives them a vesicated or 
bulbous appearance, they float on the surface in 
large masses. When fruiting they lose their 
bright green colour and become dingy, often 
yellowish and very dirty-looking. Such speci- 
mens the tyro is apt to pass by as worthless, but 
they are the most valuable in a scientific point 
of view; while the vivid green slimy masses of 
barren filaments that excite his admiration as 
