556 SUMMARY OF CURRENT RESEARCHES RELATING TO 



usually quite disappeared from the guard-cells. This phenomenon' 

 corresponds with the formation of saccharose in potatoes at a low tem- 

 perature. The lowering of the temperature of the cytoplasm appears 

 to increase its attractive force for sugar ; but the reason of this is at- 

 present unexplained. 



Effect of Mineral Salts on Assimilation.* — From a series of ex- 

 periments on Ulva latissima, E. A. Newell Arber derives the following 

 general conclusions : — Distilled water is, after a short time, fatal, owing 

 to the absence of dissolved salts ; witb tap- water, a large amount of 

 carbon assimilation takes place ; but the maximum (in the case of Ulva) 

 only with sea-water. Sodium chloride appears to be absolutely in- 

 dispensable, in the case of marine plants, for even a moderate amount of 

 carbon assimilation ; the maximum degree of concentration with this salt 

 is probably between 1 and 5 p.c. None of the other salts which form 

 the principal constituents of sea-water can take its place; and the 

 absence of any one of them, provided the others were present in normal 

 amount, did not cause any inhibition ; while the presence in distilled 

 water of either calcium sulphate or potassium chloride appears to inhibit 

 carbon assimilation almost completely. 



Excentric Growth in Thickness, j — A. Ursprung discusses this 

 subject from a mathematical point of view, and comes to the general 

 conclusion that the explanation of an excentric growth in thickness of 

 stems and branches must be sought for in mechanical forces. 



Sensitiveness of Plants to small amounts of Potassium Salts. J — 

 H. Coupin finds that plants are as sensitive to minute quantities of 

 nutrient substances (salts of potassium) in the soil as they are to minute 

 quantities of toxic substances. In the case of Bordeaux wheat, he gives 

 the following as the minimum proportions of potassium salts which 

 can be utilised by the plant: — carbonate 0-000,000,1; phosphate 

 0-000,000,25; sulphate 0-000,000,8; chloride 0,000,003; nitrate 

 0-000,004. 



Absorption of Phosphorus and Sulphur during Germination. § — 

 G. Andre states that during the first few days of germination a seed 

 will lose from 25 to 33 p.c. of its dry weight. But, while the amount 

 of organic matter has diminished, the seed will have absorbed mineral 

 substances (silica and lime) from the soil ; ihe absorption of phosphoric 

 acid and potassium taking place at a later period. In the case of the 

 scarlet-runner (Phaseolus multiflorus), the amount of sulphur (including 

 that present in the albuminoids) increases regularly, and at the time when 

 the plant has attained the original w r eight of the seed, is 2.^ times as 

 much as at the period of germination. On the other hand the amount 

 of phosphorus remains stationary, and increases only with the increase 

 in the amount of nitrogen. 



Action of Low Temperatures on the Germination of Seeds. ||- — 

 Dr. A. Jencic confirms the statement that, when seeds have been air- 



• Ann. of Bot, xv. (1901) pp. 39-69. 



t Ber. Deutsch. Bot. Ges., xix. (1901) pp. 313-26 (\ pi.). 



J Comptes Rendus, cxxxii. (1901) pp. 1582-4. Cf. this Journal, ante, p. 302. 



§ Tom. cit., pp. 1577-9. 



|| Oesterr. Bot. Zeitschr., li. (1901) pp. 2GS-9. Cf. this Journal, 1900, p. 84. 



