FEESH- WATER ALG^. 95 



Other two lochs in the vicinity did not contain the plants alluded 

 to." 



Dr. M. C. Cooke says that in July, 1884, this alga {Rivularia) 

 was sent to him from a large pond between Haslemere and 

 Farnham, where it rendered the water quite opaque, like a mixture 

 of pea-soup and water. 



Lyngbya consists of long rigid or flexuous filaments, bluish- 

 green or yellowish-green in colour, rarely branched. Some species 

 are found in large masses in boggy pools, others in the brackish 

 water. 



Class II. — Zygospores. 



In this class the plants differ greatly in the structure of their 

 vegetative body, and we are at present acquainted with but few 

 intermediate transitional forms connecting the various sections 

 belonging to it. The formation of a tissue, in the ordinary sense of 

 the term, occurs only in a few cases, the thallus being unicellular ; 

 nevertheless, there is a decided advance in the degree of 

 organisation as compared with the Protophyta. 



The Fandon?iece consist of cells which are either isolated, or 

 united into families by a gelatinous envelope, and then called 

 ccenobia. In this state they still have the power of motion, each 

 cell possessing two long cilia which protrude through the cell-wall. 



Pcvidorijia was the first instance in which conjugation of 

 zoogonidia was observed (Pringsheim), and the process is very 

 curious. Each of the sixteen cells contained in a coenobium breaks 

 up into sixteen smaller cells, the gelatinous envelopes of which 

 become softened and let the zoogonidia escape. They are green,with 

 a red spot in front, where they bear two cilia, by means of which 

 they move rapidly about. Two of them now coalesce, forming a body 

 at first constricted, then round, and of much larger size than the 

 combined zoogonidia, of which however the four cilia and the two 

 red corpuscles are still seen, but these soon dissappear. The 

 colour of the cell now changes from green to brick-red, and 

 the cell, which has greatly increased in size, breaks up and 

 allows the escape of several large zoospores. The zoospores, after 

 a short period of swarming, surround themselves with a gelatinous 

 envelope, and by successive divisions give rise to sixteen primordial 

 cells, forming a coenobium similar to the mother plant. 



