— 88 — 



Eunotia Arcus was found in practicaily every sample in 1007 

 and 1008, but was rare except during the colder period of the 

 year. In 1007 the increase began in January, suffered an inter- 

 ruption in Februaryand termina ted in April (cf. Microspora) ; 

 in 1008 the increase began already in the preceding November, 

 there was a long-sustained maximum from January to April 

 (cf. Microspora) and then a sudden decrease. In 1000 there 

 was a very faint and short maximum in March, while in 1006, 

 although présent in some quantity in the first samj)le, Eunotia 

 Arcus was absent altogether from April to November inclusive. 

 In view of its abundant development occurring only in thecold 

 part of the year an adaptation to low températures must be 

 assumed. The attainmentof the March-maximum in 1007 may 

 then be ascribed to the effects of the rather cold January and 

 February, while the decrease after Mardi may be interpreted 

 as tlie effect of the exceptional mildness of that montli. The 

 January-maximum of 1008 corresponds to great coldness of that 

 montli with a marked drop of température as compared with 

 December. The température (except for February, which is 

 however not warm enough to hâve an adverse effect) remained 

 below ihe average till May, wlien the unusually mild month 

 corresponds to a sudden decrease of the Diatom under considé- 

 ration. The faint maximum of March 1000 may hâve been eut 

 short by the exceptional températures of April. It may be 

 noticed also that in the winter of 1003-1006 (i. e. December, 

 January, February) no low températures quite like those of the 

 next two winters were realised, January even being exception- 

 ally mild, and this possibly explains the scanty représentation 

 of Eunotia Arcus in the spring of 1006. It is a little difficult 

 to account for the complète absence of the Diatom in April, May 

 and June of 1006 (unless the often-mentioned unusual concen- 

 tration of the water at thattime affected it adversely), although 

 the high températures of July and August might hâve been suf- 

 ficient to account for its absence in the suramer- and autumn- 

 months (1) . On the whole however the relation bétween the 

 frequency of Eunotia Arcus and the temperature-data is quite 

 patent. 



(1) It may also be that the stronp simshine of April 1906 and April and 

 May 1901' had something to d<> with the poor development gf Eidintin Arcus 

 in those two years. 



