Hi FRESHWATER ALG.E. 



filamentous kinds wliicli eveiyoue would recognise as first cousins of the 

 familiar green seaweeds, an immense number of minuter forms, the 

 relationship of which to their more robust kindred is not so e\adent, and 

 at least two vast groups, totally different in external aspect, rich in the 

 tcnderest colours and most exquisite shapes. 



But the whole order is especially attractive to the Botanist, not only 

 by reason of its singular gracefulness and beauty, but because in no other 

 can ho watch so easily the mysterious fundamental processes of cell- 

 division and of reproduction. " To penetrate everj'where to these first 

 rudiments of stioictiu'e, to follow out from them the coiurse of the develop- 

 ment of the tissues of all parts, and to make out the laws according to 

 which the cell-formation progi'esses to produce the various arrangements 

 on which the structure of the plant essentially depends, is one of the 

 most difficult, but at the same time most profitable tasks."* 



The facility with which these plants can be kept alive for a length of 

 time — often long enough to enable the observer to trace in one individual 

 its entire life-history — the trausluceucy of their cell walls, which lays 

 open to his observation under the microscope the active processes going on 

 within ; the many points in their moi'phology still awaiting solution, and 

 the comparative ease with which they may be preserved for an indefinite 

 period with httle loss of their natural form ; aU these are grounds upon 

 which they possess a high degree of interest, and challenge a more 

 extensive study than they generally receive. 



2nd. — Wliere are the Freshwater Alga3 to be sought ? 



One is almost tempted, from their universal diffusion, to reply, 

 "everywhere." It is, at any rate, safe to answer, " wherever moisture 

 or fresh water is to be found — on the pots and walls in a gi-eenhouse, on 

 the shady sides of tree-trunks, on damp banks, on the moist faces of old 

 walls, in the diipping from water-taps, in every ditch, in the hoof-holea 

 where cattle have trodden in marshy ground, on thatched roofs, in bogs, 

 on moist moorlands ; above all, in every clear pool, lake, and mountain 

 tarn, in cold springs and hot springs, floating on the surface of water 

 wherever it is foiind, clinging as parasites to submerged roots, sticks, or 

 larger water-plants, or entangled among bog mosses and the hke." 



In describing the principal families wo shall revert to their 

 habitats and give some hints as to the signs by which their presence 

 may be recognised. 



3rd. — Let us now proceed to consider Jjriefly the principal orders 

 into which they naturally fall, omitting, however, for convenience, 

 that vast gi'oup of minute brittle siliceous organisms, the Diatomacea3, 

 whose vegetable character was so long disputed, and is not even now 

 universally admitted, with which every Microscopist is familiar, inas- 

 much as their amazing variety of form and the great beaiity of their 

 sculptured marltings have long caused them to stand foremost among 

 the prepai'ations ot dealers and the objects of popular exhibition. 



We begin, therefore, with the large and universally distributed 

 division of Unicellular Algaa, which form (with the exception of the 



* A. Braun. "The rhenomenon of Rejuvenescence in Nature," p. 122, (Ray 

 Society, 1853.) 



