158 



Chlorophycece 



6 - 8 7 "3 p.) and P. suboctangulare West (length 10'7 11 -5 p; breadth 6'8 

 7 n ; fig. 55 E). The cell-wall of many of the species is of a yellow or reddish- 

 brown colour. P. minutum 

 (Ralfs) Cleve is relatively the 

 longest species of the genus, 

 but should, perhaps, be rele- 

 gated elsewhere. 



Tribe 4. Closteriece. 



The cells are elongate, 

 generally curved, and usu- 

 ally attenuated towards 

 each extremity. There is 

 no trace of a median con- 

 striction and the plants are 

 circular in transverse sec- 

 tion. The points of division 

 are always in the middle 

 region of the cell and the 

 cell-wall usually possesses 

 pores. The cells are only 

 symmetrical in one longi- 

 tudinal plane. 



Genus Roya West & 

 G. S. West, 1896. This 

 genus was named after the 

 late Dr John Roy, who first 

 pointed out the differences 

 between those plants which 

 are now included in it and 

 species of Closterium. The 

 cells are elongate, cylindri- 

 cal, very slightly curved and 

 scarcely attenuated to wards 

 the poles. There is only 

 one chloroplast which occu- 

 pies almost the entire cell- 

 cavity. It extends to within 

 a very short distance of 

 each pole and its extremi- 

 ties are convex. In the 



Fig. 55. A and B, Fenium Cylindrus 

 (Ehrenb.) Breb. ; A, from Loch Minnoch, 

 Kirkcudbright; B, zygospore from Thursley 

 Common, Surrey ( x 474). C, P. spirostrio- 

 latum Barker, from Kerry, Ireland (x474). 

 D, P. Libellulu (Focke) Nordst., from Bowness, 

 Westmoreland ( x 200). E, P. suboctanciulare 

 West, with zygospore, from Killarney, Kerry, 

 Ireland ( x 365). F, P. curium Breb., from 

 Grimspound, Devonshire ( x 474). G and 

 H, Roya obtusa (Breb.) W. & G. S. West 

 var. montana W. & G. S. West, from Baildon 

 Moor, W. Yorks. ( x 570). I, R. Cambrica 

 W. & G. S. West, from Llyn Ogwen, N. Wales 

 (x474). J and K, R. Pseudoclosterium (Roy) 

 W. & G. S. West, from Pilmoor, N. Yorks. 

 (x474). 



