2 BRITISH DESMIPIACE7E. 



of fresh water, and they constitute the family 

 DIACE/E of the order CONJUGATE. The Algae are a class 

 of plants which possess a simple structure, the most 

 highly developed forms being the red Algre (or 

 Floridese), which are almost entirely marine. 



Although some Desmids possess cylindrical cells 

 very similar to those of other families of Conjugatse, 

 they can he readily distinguished by peculiarities in 

 their cell-structure, their method of division, and the 

 formation of the zygospore. 



Some few Algae are subaerial, occurring in moist, 

 shady places, and among these are a few Desmids, 

 principally species of the genera Mesotdenium. and ('////?/- 

 drocystis. 



The Desmids are free-floating, and often occur 

 in mucilaginous masses. They are never marine, but 

 have been found, though rarely, in slightly brackish 

 water. They exhibit great diversity in size, the 

 longest axis varying in length from 8 to 1200 ft. In 

 the British genera Hyalotheca, Gfymnozyga, ^pouJi/lo- 

 sium, Sphaerozosma, Onychonema, and Desmidium, the 

 cells remain attached to each other after division in 

 the same manner as in the other families of Conjugatse. 

 These filaments may be plane or twisted, and the cells 

 may be connected by their flat apices or by the 

 apposition of corresponding apical projections. This 

 filamentous condition may however be developed in 

 species of genera which normally occur as single cells. 

 Instances of this are known in Cosmarium, Euastmm, 

 Micrasterias, and N<inr<ixt'rum. The cells of the genera 

 (-i<nif<t<>::i/{/<>ii and (Jniir/ilnrin frequently occur in long 

 filaments, but a very slight disturbance is sufficient to 

 cause the dissociation of these filaments into their 

 separate cells. Even in the more typical filamentous 

 forms such as Desmidium, Hyalotheca, Sphaekozosma, 

 and Oiii/clioncuHi, the filaments are usually dissociated 

 into individual cells just prior to conjugation. 



Every person who for the first time examines a 

 varied collection of Desmids is astonished at their 



