THE MAUIXE ALGJ, OF (iUERNSEV 31 



(7) Temperature. 



*' The mean winter temperature of the atmosphere is 6 degrees 

 higher than tliat of Greenwich, the summer temperatvu-e being rather 

 cooler. The mean temperature is 2| degrees higher than that of 

 Greenwich " (Black). As the temperature of the Island has a range 

 of 8 degrees, this comparative equa))ility has a distinctly favourable 

 effect on the growth of Alg;e, especially those exposed for several- 

 hours by the falling tide. The average annual sunshine is 42 per 

 cent., and the average sunshine per day is 5 hours ; the average rain- 

 fall in the island is about 29 07 inches (CoUinette). 



According to Rattray, temperature has a distinct influence in 

 hastening the production and emission of spores and prolonging the 

 reproductive capability of Algie. The maintenance of an even and 

 mild climate must therefore assist in promoting the marine fertility 

 of this island. Harvey noticed *' how those small and delicate kinds 

 which grow within tide-marks are found in greater luxui-iance or in 

 more abundant fruit in a warm than in a cold season." He also 

 remarked "how Pf^f//;irt P«yo/i/rt attains in warm summers on the 

 south coast of England a size as large as it does in sub-tropical lati- 

 tudes, while in a cold season it is dwarfed and stunted." The summer 

 of 1912 was exceptionally cold and wet, and the specimens were then 

 plentiful, but small in size. 



With regard to the temperature of the sea, Dickson has observed 

 that *'the upper layers of w^ater from 3 to 5 fathoms are apparently 

 subject to temporary local weather conditions which may or may not 

 produce a distribution similar to that formed underneath." At a 

 depth varying from 17 to 80 fathoms, this writer has reported the 

 temperature to be 50-S to 54 C. 



IV. Arrangement. 



(a) Terminology. 



Owing to differences of opinion as to the exact definitions of the 

 various tei-ms employed in marine ecology, I have restricted myself 

 to the use of such geographical expressions as '^ Beg ion " and "Zf>;<e" 

 oY'-BeUr 



'' Beg ion,"" as used by Kjellman, is a term universally accepted to 

 denote a portion of the shore with relation to the tide. He divided 

 off the algal vegetation into three regions : — " 1. The Littoral region 

 stretches between the high-tide and the low-tide mark, and includes 

 man}" Green algse, Brown algae, and some Red algse. 2. The Suh-^ 

 littoral ranges from below low-tide mark down to a depth of 

 20 fathoms (40 metres). Here algse of all three colours are repre- 

 sented, but Green algfe cease, and Red algse become more numerous 

 with increased depth. 3. The E-littoral region is below the pre- 

 ceding and descends as deep as light; it is poorer in species and indi- 

 viduals — the latter are smaller and distorted. There is also a charac- 

 teristic underlying vegetation of epiphytes requiring less light." 



''Zone'' or ''Belt'' indicates the lateral continuity of a genus 

 or species along the shore. There is often over-lapping and inter- 

 mingling of alga^ in the respective zones ; those (^f one zone may form 

 undonzroAvths of others. 



