270 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Algse. 



Rabenhorst's Cryptogamic Flora of Germany (Algse).* — Parts 

 6 and 7 of Dr. Hauck's ' Marine Alg«,' in Rabenhorst's ' Crypto- 

 gamic Flora of Germany, Austria, and Switzerland,' complete the 

 account of the Floridese with the CorallinaceaB, and commence the 

 Pbseophycese, wbicb be divides into tbree orders, tbe Fucoidese, 

 Dictyotacese, and Pbseozoosporese. Tbe small number of species 

 comprised in tbe first two orders are described, and tbe Pbaeozoosporese 

 commenced. Tbe families included are tbe Ectocarpacese (including 

 SpJiacelaria), Mesogloeaceae, Punctariacese, ArtbrocladiacesB (tbe single 

 genus Arthrocladia), and a commencement of tbe Sporocbnacese. 



Distribution of Seaweeds.f — A. Piccone gives a number of 

 details witb respect to tbe mode of life and distribution of marine 

 algse. As a rule, tbey are entirely confined to tbe coasts ; altbougb 

 sbells of diatoms are found abundantly at great deptbs, it is doubtful 

 wbetber tbey bave lived tbere, or wbetber tbe sbells bave been carried 

 by currents. Tbe gulf-weed tbe autbor tbinks does really vegetate 

 in tbe deptbs of tbe " sargasso-sea.'^ 



Tbe physical nature of tbe sea-bottom, wbetber stony, sandy, or 

 muddy, exercises considerable influence on tbe distribution of sea- 

 weeds, as also on tbeir external form, and especially on tbeir mode of 

 attachment. Of this tbe author distinguishes tbree kinds : — attach- 

 ment-disks, wbicb occur only where the bottom is rocky or stony ; a 

 tow-like decomposed base and root-fibres ; and a pseudo-parasitism 

 on other algse. Seeing that algse derive no nourishment from tbeir 

 substratum, its chemical nature is indifferent. 



As regards the purity of the water, a medium quality appears to 

 be most favourable to the growth of seaweeds. A considerable 

 influence is exerted by the varying density at different deptbs ; and, 

 as with land-plants, each species has its optimum temperature. The 

 presence of light is indispensable to their growth ; but it entirely 

 ceases only with the absence of tbe chemical rays. Direct sunlight is 

 more favourable to the growth of green, shade to that of red or brown 

 algse. Light has also an influence on tbe production and movement 

 of zoospores, and on the heliophobic tendency shown by many 

 fertilized ova. 



Only those algse wbicb grow in shallow localities follow tbe 

 movements of waves, and various species establish themselves in 

 protected spots or those exposed to tbe surf, or according to the 

 nature of the bottom. A great flow and ebb of tide is unfavourable 

 for marine vegetation. Tbe influence of marine currents is very 

 great on the distribution of species. 



Tbe dissemination of spores is brought about chiefly by marine 

 currents ; but tbe author believes that tbeir unequal specific gravity 

 is not without importance in this respect. It is probable that they 

 are also transported by fish, attached externally, or even after having 

 been swallowed. 



* Rabenhorst, L., ' Kryptogamen-Flora von Deutschland, Oesterreich u. d. 

 Schweiz. 2"*'' Baud, Die Meeresalgen von F. Hauck, Lief. 6-7.' 



t Chron. Lie. Christ. Colombo, 1883. See Bot. Oentralbl., xvi. (1883) p. 289. 



