NOTES OX THE ALG^ OF LETCESTERSHIEE 2G7 



May 29/16. S. tenuissima (Hass.) Kiitz. was found reproducing on 

 May 31/13 at Swithland, and on May 19/14 at Scraptoft. From a 

 comparison of these dates with those previously noted, it would appear 

 that in the latitude of the East Midlands reproduction in ^piroqyra 

 takes place just a little later than it does farther south. This looks 

 as though temperature must be one of the most important factors in 

 bringing it about, and this is further exemplified by the influence of 

 the very warm January of 1916. In Febi-uary of that year at least 

 two Spirogvras were found with zygospores, viz. ^'. Weheri and 

 8. Orevilleana. So early an apj^earance of conjugation is verv 

 unusual. 



Sirogoniiim siicticum Kiitz. is not a very common alga, but was 

 found in quantities in three different parts of the county^ — Shaker- 

 stone Canal, May /13, conjugating ; near Castle Donington, May /13, 

 conjugating and forming zygospores ; Sutton Wharf, June /lo, 

 zygospores. It was not observed in any of -the other samples 

 extmined. 



The Desmids collected by Bates were examined and described by 

 John Koy of Aberdeen. He says (Fl. Leicestersh. 327): "The 

 species are not nearly so numerous as might be expected considering^- 

 the number of localities examined," but the localities to which he 

 refers are, after all, fairly near one another. He would be still more 

 astonished could he see the far smaller number now collected from an 

 area many times as large. He remarks on the entire absence of 

 the genera Desmidiiim, Sjyom/j/Iosium and Xanihidium — of these, 

 Spondylosium papUlatum has now been found (Colery Eeservoir, 

 June /14). The best-represented genera are Cosmarium and CIos- 

 terium. Cosmarium Botrytis Menegh. is perhaps the commonest 

 species, but C. Meneyhinii Ereb. is also widely distributed. Clns- 

 tcrium moniliferum Ehrenb. is frequently found, and this is true of 

 C. ucerosicm (Schrank) Ehrenb. and of C. venus Kiitz. The only 

 three forms of wliich zygospores have been found are : — Closterium 

 rostraium Ehrenb., July /14, Cosmarium Botrytis Menep-h. var. 

 paxillosporum, June /14 and Arfhrodestmis incus (Breb.) Hass., 

 June /1 4. Closterium moniliferum Ehrenb. has been observed in all 

 months of the jaar, but most commonly in Maj'. C. acerosum. 

 (Schrank) Ehrenb. occm's from A})ril to September, but again most' 

 commonly in May. Hoy speaks of Micrasterias denticulata, Tef- 

 viemorus Icevis, and Penium curtum as being "very numerous," but 

 not a single specimen of either has been found in the recent collections. 

 The genus iitaitrastrum is undoubtedly less well rej)i'esented now 

 (though it is still one of the three commonest genera). S])ecies of 

 Euasfrum are certainly rarer, and the genera Mesofcenium, CijUndro- 

 cystis, Bocidium, Gonatozyyon, and Hyalotheca, recorded by Bates, 

 have not so far been found at all. 



It seems evident, therefore, that Desmids are not so prevalent in 

 the county as they were thirty years ago. What is the cause of this y 

 Mr. Horvvood (Crypt. Fl. Leicestersh. in Trans. Leicester Lit. Phil. Soc;. 



xiii. 35, 1909) says : " In the region of Charnwood Forest 



neighbouring collieries have wrought sad havoc by reason of the 

 volumes of smoke, dust, steam, and injurious gases contiiuiallv bein^' 



