160 



and the apical vacuoles are often correspondingly lengthened out. 

 The chloroplasts are similar in form to those of the genus Penium. 

 consisting of an axile mass with more or less distinct longitudinal 



Fig. 56. A, Closterium acerosum (Schrank) Ehrenb., from Glen Shee, Perthshire 

 (x200). B D, Cl. striolatuni Ehreub., from Frensham, Surrey; B and C, 

 outlines, x 125 ; D, x 260. E, Cl. acutinn Breb., from Sligachau, Skye ( x 474). 



F, Cl.parvulum Nag., zygospore, from Esher West-end Common, Surrey ( x 474). 



G, CL rostratum Ehrenb. var. brevirostratum West, zygospore, from Wimbledon 

 Common, Surrey ( x 200). 



ridges. In Cl. acutum Breb. and several others there are no 

 longitudinal ridges. 



The curvature of many of the species of this genus is very 

 constant and may be utilized as a specific character. In stating 



