DESMID FLORA OF A TRIASSIO DISTRICT. 141 



The Census List at the end of this paper adds 122 species 

 and varieties to the Desmid flora of Devonshire, bringing it up 

 to a total of about 500 species and varienes, collected principally 

 from the districts of East Devon and Dartmoor. Zygospores 

 when observed have been specially noted in the list in connection 

 with their respective species, principally because they occurred 

 in the vernal gatherings, and the assumption hitherto has been 

 that zygospores were more or less an autumnal production. 

 They appear to be freely produced by some species as early as 

 March and April, in fact it was not uncommon to find them 

 present in gatherings made in the winter months, and in such 

 a condition as would indicate that they were the result of recent 

 conjugation. With the view of obtaining some knowledge of 

 the continuance of the vegetative stage of Desmids through the 

 winter months gatherings were made from the bogs on Beacon 

 Hill and Harcombe and the material when worked out compared 

 with gatherings made in late spring and early summer of the 

 previous two years. The winter gathering on Beacon Hill 

 yielded 50 per cent of the summer gathering in species and varie- 

 ties, and the bog on Harcombe also 50 per cent, of the summer 

 total. In considering these figures, however, it should be re- 

 membered that whereas the summer lists were made from several 

 gatherings of considerable bulk, the winter lists are from one 

 gathering only and that not a large one. It would appear that 

 most species in a southern county like Devonshire pass the winter 

 in the vegetative state. 



Two Desmids are conspicuously absent from East Devon 

 {i.e. from the present collecting stations), Euastrum cuneatum 

 Jenn. and Euastrum insigne Hass. Their absence is very un- 

 accountable, as they are widespread on Dartmoor and also in 

 the New Forest, indeed Euastrum cuneatum occurs so abundantly 

 in some of the New Forest bogs that one is inclined to regard 

 it as a lowland species. 



Where the specific dimensions have been found to differ 

 materially from those given in West's Monograph of the British 

 Desmidiaceae (11), a note has been made of the fact by giving 

 the measurements in brackets, these measurements extending 

 the ranges of specific limitations given in the monograph either 

 in a maximum or minimum direction. 



The nomenclature throughout is that adopted by the Wests 



