32 PLANT-LIFE 



minute plant forms are of singular beauty; they are 

 classed with the Green Algse (Chlorophycese). Over 

 1,000 species have been distinguished, all of which 

 occur in fresh water. Some species are found in ponds, 

 but as a rule these plants thrive best in open situations, 

 so that Highland lochs and moorland and bog pools are 

 the best hunting-places. Some are found free in the 

 water, and can be secured with a fine net; others are 

 attached to plants or the muddy bottom of the pool. 

 Sunlight generally attracts them to the surface. When 

 very numerous, they give a green tint to the water. 

 There are many one-cell species, but multicellular forms 

 occur in which the cells are attached in rows, and so 

 form threads, or filaments. It should be noted, however, 

 that the cells of the threadlike forms exhibit the habits 

 of the one-cell forms, and it is questionable whether such 

 forms should be regarded as multicellular plants: the 

 thread might rather be looked upon as a series of one- 

 cell plants, which are independent units in all points 

 but that of their attachment in rows. 



The Desmid cell, which exhibits great variety of form 

 in different species, almost invariably displays two quite 

 symmetrical halves, which are very frequently marked 

 off from each other by a constriction forming a sort of 

 neck, or waist, between them. The cell-wall, which is 

 often sculptured, lobed, covered with protuberances, and 

 furnished with pores, is in two halves or valves, the edges 

 of which meet at the constriction, or median plane. 

 The cell-nucleus occurs in the median plane, and a 

 colour-bearing body (chromatophore), which may be 

 radiate in form, or composed of several plates, occupies 

 the greater part of each half of the cell. Pyrenoids, 



