Physiologie. — Algae. 513 



For determining the real assimilation under any conditions 

 a valuation of the concurrent respiratory carbon dioxide pro- 

 duction was essential. At low temperature this is small in pro- 

 portion to the assimilation, but at moderately high temperatures 

 it is much increased. A satisfactory series of determinations of 

 the assimilatory maxima for the whole ränge of temperature 

 was obtained. The amount is just determinable at — 6° C. and 

 then rises rapidly with higher temperatures giving a curve which 

 is convex to the temperature abscissa. The curve is similar to 

 that accepted for the effect of temperature on respiration and 

 rises more and more steeply at higher temperatures up to 38° C. 

 At this temperature the leaf is incapable of maintaining its 

 high rate of assimilation for any long time and the higher the 

 temperature the shorter is the duration of the period of maxi- 

 mal assimilation. 



After the optimum at 38° C. a rapid decline takes place to 

 the maximal temperature of 45° C. — the fatal temperature for 

 the leaves used. E. Drabble (London). 



WOOD a n d Berry , Selection of seed by chemical 

 methods. (Proc. Cambridge Phil. Soc. Vol. XII. Part II. 

 1903.) 



Observations on beets, swedes and mangels. 



The distribution of the sugar Contents of the mangel was 

 determined and was shown to be much denser towards the 

 periphery. In swedes the sugars are cane sugar, dextrose 

 and levulose in such proportions that the juice has practically 

 no rotatory power. The results for mangels show that the 

 percentage of dry matter in individual roots of the same variety 

 grown side by side varies greatly. The series is made up of 

 a few roots with very low values, a few with very high, and a 

 large number intermediate between the two, rising by short 

 steps from the lowest to the highest limit. While there is a 

 distinct tendency for the percentage of dry matter to be higher 

 in small than in large roots the inverse proportion between the 

 size of the root and the dry content is by no means definite. 



The Variation amongst individual swedes is similar in 

 every way to the Variation amongst mangels. 



Selected seeds from the various samples are now being 

 grown. E. Drabble (London). 



G0M0NT, M., Sur la Vegetation de quelques sources 



d'eau douce sous-marines de la Seine-Inferieure. 



(C. R. Acad. des Sciences Paris. 25 janv. 1904. p. 221— 223.) 



On trouve, au pied des falaises dela Seine-Inferieure, des 

 sources d'eau douce qui debouchent pres de la limite superieure des 

 marees ou situees plus bas, ces dernieres restant moins longtemps ä 

 decouvert. Toutes offrent un caractere commun remarquable, l'absence 

 de Coralline'es et de Fucacees. Les sources les plus eloignees de la mer 



Botan. Centralblatt. ßd. XCV. 1904. 33 



