101G SUMMARY OF CURRENT RESEARCHES RELATING TO 



enable tho starch-containing cells to transform their starch into sugar, 

 which is then carried to the part when! growth recommences, and 



the period of rest is thus closed. This is true of such structures as 

 potatoes, and of the leaf-huds of deciduous trots. 



Resistance of Plants to Drying 1 .* — Herr G. Schroder has investi- 

 gated the extent to which plants belonging to various divisions of the 

 vegetable kingdom will retain their vitality under prolonged desicca- 

 tion. Among flowering plants succulent plants or parts of plants 

 possess this property to the greatest degree. Many seeds also retain 

 their power of germination after being kept perfectly dry for months, 

 or even for many years. Many mosses and some algas sliow a 

 remarkable power of retaining their vitality under complete dryness; 

 as also do the spores of fungi and some Schizomycetes, while the 

 hyphae of fungi perish rapidly when deprived of water. 



Respiration of Plants.* — MM. G. Bonnier and L. Maugin describe 

 more at length the experiments on which they found the conclusions 

 already reported of the variation of the amount of respiration at 

 different periods in the life of the plant. 



Circulation of the Sap.$— Prof. E. Godlewski criticizes the almost 

 wholly physical explanations which have been hitherto given of the 

 movement of the sap. Bohm, and especially R. and Th. Hartig, have 

 shown that the sap ascends, not by tlie peripheral, but by the central 

 portion of the wood. Bohm and Hartig have further demonstrated 

 (1) that the pressure within the fibres and vessels is less than one 

 atmosphere, and (2) that in the same tree, the pressure is always less 

 above than below, and have tried to explain the upward movement by 

 reference to this difference of pressure and to capillarity. In criti- 

 cizing this theory, Godlewski maintains that it will in no way account 

 for the ascent of the sap to the heights attained in most trees. He 

 finds an explanation in the properties of the protoplasm of the living 

 cells. The cells of the medullary rays and of the wood-parenchyma 

 pass on the sap, step by step, to the mesophyll of the leaves. Many 

 botanists have allowed that the phenomena of root-pressure are not 

 confined to the root ; the author maintains that the phenomena are 

 precisely similar in the central cylinder of the stem. In explanation 

 of the entrance and exit of the sap, Sachs had emphasized that the 

 layer of protoplasm round the internal walls of the cells had not the 

 same structure on all sides : where the cell touches other cells, the 

 layer of protoplasm is readily permeable by water passing in by 

 osmosis, but presents great resistance to the passage of water under 

 jji-essure ; but where the cell is in contact with a vessel or fibre, its 

 protoplasmic membrane readily allows water to pass through it under 

 the influence of pressure. Sachs thinks that this difference in the 

 structure and properties of the protoplasmic layer enables the cell to 



* Arbeit. Bot. Inst. Tubingen, ii. (1S86) 51 pp. See Naturforscker, xix. 

 (18S6 p. 398. 



t Ann. Sci. Nat. (Bot.), ii. (1885) pp. 315-80. Cf. this Journal, ante, p. 051. 



| Arch. Slav, de Biol., i. (1886) pp. 9-22. Cf. this Journal, ante, pp. 283, 477, 

 653. 



