360 PROCEEDINGS OF THE 



a set of five Zeiss apocliromats, a lamp, and some valuable 

 slides. The thanks of the Club were accorded to Mr. John Tryon 

 for this valuable gift. The President drew the attention of the 

 members to the rule with regard to smoking at the meetings, as 

 complaints had been made that it had not been observed. 



The President then called on Mr. J. Wilson to give " A Short 

 Account of the genus Closterium." Mr. Wilson said that he had 

 frequently noticed that at the excursions the majority of the 

 members were content to describe their " finds " as " Desmids," 

 making no attempt to determine the species. He attributed this 

 to the scarcity of literature on the family, but said that since the 

 publication by the Ray Society of the Monograph on the 

 Desmidiaceae by the Wests, identification had been considerably 

 facilitated. He proposed to deal only with the genus Closterium. 

 Desmids are minute plants, bright green, and of great diversity 

 of form, and are found only in fresh water. Those of the genus 

 Closterium are cylindrical, and attenuated from the middle 

 towards the extremities, and all are more or less curved. They 

 have an inner cell-wall of pure cellulose, and an outer one more 

 thickened, often brownish and impregnated with various salts. 

 The cell- wall is either smooth or ribbed in various ways. These 

 characteristics are of specific value, but the shape of the cell is 

 more important. In Closterium there are two chloroplasts, a 

 central nucleus, and a vacuole at each end of the cell containing 

 moving granules. The position of the pyrenoids in the chloro- 

 plasts is a distinguishing feature. The Desmid is enclosed in a 

 mucilaginous sheath, which it secretes. Desmids multiply in three 

 different ways. (1) By cell division : When the nucleus divides, 

 a cell- wall is formed, and after separation each half of the Desmid 

 grows a new semi-cell, thus regaining its characteristic shape. (2) 

 Conjugation : In this case two cells surround themselves with 

 mucilage, and the contents pass out from the middle of each and 

 coalesce, forming a zygospore. The zygospore ultimately divides 

 twice, and forms two protoplasts, which eventually burst the cell- 

 wall, and when free rapidly grow and assume the usual shape of the 

 species. Desmids move towards the light, and advantage is taken 

 of this fact in separating them from the sediment with which they 

 are usually collected. Desmids are found in all sorts of pools, 

 from lakes to the water in cart tracks. They are often found 

 adhering to submerged plants, and especially to the sphagnum in 



