824 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Turgidity of the Pith and Leaf.* — Ilerr J. Bohm assigns reasons 

 for believing that the turgidity of tho pith is not tho result of hydro- 

 static prcssuro in tho colls, but of tho swelling of the cell-walls, and 

 especially of tho longitudinal walls. The samo is also truo of leaves. 

 Experiments woro made chiefly on cylinders of the pith of tho sun- 

 flower and tobacco. Cylinders of tho latter, which, on drying, had 

 lost 30-40 per cent, of their weight, usually became, when placed in 

 a diluto solution of nitro or sugar, as stiff as icicles, although thoy 

 often did not attain their original weight or length. If dried too 

 quickly, they acquired much more than their original weight, even if 

 placed in distilled water, without, however, becoming rigid ; and 

 this was always tho caso with porfectly whito cylinders of the pith of 

 tho sunflower. 



Influence of Light on the Structure of Leaves and number of 

 Stomata.t — M. L. Dufour has determined, by experiments on a 

 number of plants, that in strong direct sunlight tho number of stomata 

 on a unit of surface is larger, and the transpiration is more abun- 

 dant, than in diffused light. Ho further states J that leaves fully 

 exposed to tho sun have a larger surface than those growing in tho 

 shade, and that the same is true of tho epidermal cells; that, in 

 proportion as leaves dovelope, thoy acquire fresh stomata up to an 

 advanced period in their evolution. It is the adult leaf last formed 

 which has the largest surface, the most cells, and tho largest numbor 

 of stomata. 



M. L. Mer § confirms these statements and regards the formation 

 of stomata as due, in most cases, to a local multiplication of 

 epidermal cells, followed by an arrest of development. 



Influence of Water on the Number of Stomata. || — M. J. Cos- 

 tantin has shown, by transplanting plants from one medium to another, 

 that a direct influence is exerted on the number of stomata, those on 

 leaves produced in the air greatly exceeding thoso on leaves produced 

 in the water in the same plant. A rhizome of Polygonum amphibium 

 was divided into two, and the two parts placed under precisely 

 similar circumstances, except that one was grown in the water, the 

 other in the air. The latter had a number of stomata on the lower 

 surface of tho leaves, the former none at all. 



Biology of Unilateral Infiorescences.1I — Dr. J. Urban discusses 

 the causes of the unilateral arrangement of the flowers in many 

 inflorescences, which he arranges under the following heads, viz. 

 Movements in the flower-stalks and in tho axis of the inflorescence ; 

 Suppression of flowers on one side of the axis ; Monochasy, either 

 pure or resulting from the reduction of cymes. 



* Bot. Ztg., xliv. (1886) pp. 257-62. 



t Bull. Soc. Bot. Fiance, xxxii. (18S5) pp. 385-90. 



J Ibid., xxxiii. (188C) pp. 92-5. § Ibid., pp. 122-6. 



|| Ibid., xxxii. (18SG) pp. 259-64. 



H Ber. Deutscb. But. Gescll., iii. (18SG) pp. 400-32 (1 pi.). 



