CHARA VULGARIS. 23 



The relative size of the cortical-cells is very variable, those of 

 the primary and secondary rows being in some forms almost 

 equal in diameter and prominence, while in others the secondary 

 are double the diameter of the primary. The size of the spine- 

 cells is also variable, ranging from mere papillae to well-developed 

 spines, sometimes even considerably longer than the diameter 

 of the stem. The bract-cells and bracteoles also vary much in 

 length. The stipulodes are normally rather short and particu- 

 larly regular. The stipulodes, spine-cells and bract-cells are all 

 more or less obtuse. 



The plant often occurs in bogs and in very shallow running 

 water, when it presents a tufted state (C foetida var. condensata, 

 Breb., C. coarctata Wallman), through the shortening of the 

 internodes. 



C. atrovirens Lowe, in ' Trans. Camb. Phil. See' VI, p. 551 

 (1838), an imincrusted form with several elongated ecortioate 

 segments to the branchlets, has been found in a few localities in 

 this country. 



We have not seen any specimens with black oospores (var. 

 melanopyrena Braun), the membranes of those from East Bridge- 

 rule, Cornwall, previously referred to this variety, being found 

 upon examination by transmitted light to be brown, as in other 

 forms, although appearing black to the naked eye. 



In a few instances the variations are obviously due to con- 

 ditions of growth, but in most cases the causes are not apparent. 

 For instance, it not infrequently happens that when this species 

 occurs in several pits close together, of approximately equal 

 depth and size, so that the conditions are apparently precisely 

 similar, while the individual plants of a pit will be almost identical, 

 those of each of the pits will present a slightly different facies. 



The four forms which we have characterized and figured as 

 varieties appear to us the most noteworthy, but it cannot be 

 claimed that these are always stable nor that a definite line can 

 be drawn between them. They may well be regarded merely 

 as extremes of variation. 



Braun used the name C.fcetida for this species, and his example 

 has been widely followed on the Continent, but we have thought 

 it right to retain the Linnean name. Although probably what 

 we now know as C. fragilis and C. delicatula were also originally 

 included in the name by Linnseus, owing to his not distinguishing 

 them, there can be no doubt that he was famiUar with the present 

 plant, it being the most conspicuously common species in Europe, 

 and Vaillant's figure, which is quoted in ' Species Plantarum,' 



