276 MICROSCOPIC rORMS OF VEGETABLE LIFE. 



are several Desmidiacese which nevei' make their appearance in 

 the same pools for two years successively, although their spo- 

 rangia are abundantly produced, — a circumstance which would 

 seem to indicate that their sporangia give origin to some dif- 

 ferent forms. It is a subject, therefore, to which the attention 

 of Microscopists cannot be too sedulously directed. 



171. The Desmidiacese are not found in running streams, 

 unless the motion of the water be very slow; but are to be 

 looked for in standing, but not in stagnant waters. Small shal- 

 low pools that do not dry up in summer, especially in open ex- 

 posed situations, such as boggy moors, are most productive. 

 The larger and heavier species commonly lie at the bottom of 

 the pools, either spread out as a thin gelatinous stratum, or col- 

 lected into finger-like tufts. By gently passing the fingers be- 

 neath these, they may be caused to rise towards the surface of 

 the water, and may then be lifted out by a tin box or scoop. 

 Other species form a greenish or dirty cloud upon the stems and 

 leaves of other aquatic plants ; and these also are best detached 

 by passing the hand beneath them, and " stripping" the plant 

 between the fingers, so as to carry off" upon them what adhered 

 to it. If, on the other hand, the bodies of which we are in search 

 should be much diff'used through the water, there is no other 

 course than to take it up in large quantities by the box or scoop, 

 and to separate them by straining through a piece of linen. At 

 first nothing appears on the linen but a mere stain or a little 

 dirt ; but by the straining of repeated quantities, a considerable 

 accumulation may be gradually made. This should be then 

 scraped off with a knife, and transferred into bottles with fresh 

 water. If what has been brought up by hand be richly charged 

 with these forms, it should be at once deposited in a bottle ; this 

 at first seems only to contain foul water ; but by allowing it to 

 remain undisturbed for a little time, the Desmidiacese will sink 

 to the bottom, and most of the water may then be poured off, to 

 be replaced by a fresh supply. If the bottles be freely exposed 

 to solar light, these little plants will flourish, apparently as well 

 as in their native pools ; and their various phases of multiplica- 

 tion and reproduction may be observed during successive months 

 or even years. If the pools be too deep for the use of the hand 

 and the scoop, a collecting-bottle attached to a stick (§ 143) may 

 be employed in its stead. The "ring-net" may also be advanta- 

 geously employed, especially if it be so constructed as to allow 

 of the ready substitution of one piece of muslin for another 

 (§ 143). For by using several pieces of previously-wetted muslin 

 in succession, a large number of these minute organisms maybe 

 separated from the water ; the pieces of muslin may be brought 

 home, folded up in wide-mouthed bottles, separately, or several 

 in one, according as the organisms are obtained from one or from 

 several waters ; and they are then to be opened out in jars of 

 filtered river-water, and exposed to the light, when the Desmi- 

 diacete will detach themselves from it. 



