8 YORKSHIRE NATURALISTS' UNION. 



2,000 feet. The best results were obtained, however, from 

 small, permanent, peaty pools containing Sphagnum pluniosuin 

 and S. contortum, and from some of those rocks over which the 

 water incessantly trickles. It might not be amiss here to em- 

 phasize the importance of these gatherings from vertical wet 

 rocks, as many of the rarest Desmids and the best Myxo- 

 phycese are to be obtained from the gelatinous material of various 

 colours coating the surfaces of rocks constantly kept moist by a 

 thin film of water. The moorlands stretching in a westerly 

 direction from Ilkley and Keighley are not so rich as the more 

 northern districts, and present a sameness and specific uniformity 

 which is markedly absent from the latter. 



The most productive grounds for Desmids are those of the 

 Central Plain, the commons at Pilmoor, Strensall and Riccall 

 being parts of the primseval boggy country, and both in their 

 topography and alga-flora are very similar to the commons of 

 south-west Surrey. Unfortunately, Strensall Common has now 

 been drained for military purposes, and nearly all its former 

 treasures have gone. Pilmoor, near Thirsk, is probably the 

 richest locality in Yorkshire for Desmids, above 130 species 

 having been found there, among which were many very rare 

 ones: Cocket Moss, near Giggleswick, is also a very rich 

 locality for this family of Conjugatse, and a boggy place about 

 two miles south of Clapham, on the way to Rowland Knotts, was 

 also productive of many uncommon Desmids. The best gather- 

 ings from both Pilmoor and Cocket Moss were obtained from 

 UUicularia minor. The bogs and springs of Upper Teesdaie 

 were found to be exceptionally rich in many of the uncommon 

 species. 



The largest natural sheet of water in the county is Hornsea 

 Mere, but it is comparatively poor in algae, being similar in that 

 respect to the rest of the low-lying land in the East Riding. 



The list of algse published in Lees' 'Flora of West Yorkshire' 

 (1888) was very hurriedly put together; it was followed by 

 several other papers and notes referring to the algae of Yorkshire, 



Trans. Y.N.U., 1896 (puV. Aug. 1900). Bot. Series, Vol. 5. 



