406 Prof. H. Marshall Ward. The Relations between 



immediate requirements of the living protoplasm, into the form of 

 reserve starch, &c, by the protoplasm.* 



At certain periods, therefore, the cells may contain relatively large 

 quantities of this soluble, nutritions, and easily oxidised glucose. 



We have still to refer shortly to another set of events taking place 

 in the normal living cells, the connexion of which with the above 

 simultaneous functions will be obvious. This is the passage of water 

 fi-om one cell to another, a process depending essentially upon the 

 modified evaporation — transpiration^ — going on at those surfaces of 

 the cell walls which are in contact with the air in the intercellular 

 spaces, &c, and the rapidity and magnitude of whose movements 

 depend on a variety of circumstance. 



This water comes from the vascular system, by which it is brought 

 up from the soil after being absorbed by the root-hairs, and it contains 

 traces of the necessary mineral salts — chiefly sulphates, nitrates, and 

 phosphates of calcium, magnesium and potassium, in small, and 

 varying quantities — as well as dissolved gases. Whether the oxygen 

 dissolved in the water absorbed at the root reaches the cells higher up 

 in the plant or no, it is at least clear that the water in these cells 

 becomes oxygenated by contact with the atmospheric air which pene- 

 trates into the intercellular spaces, via the stomata and lenticels.£ 

 Moreover, it is impossible to doubt that oxygen reaches the water in 

 the cells'from the assimilating chlorophyll corpuscles. However, we 

 are not confined to inferences in this connexion, since Pfeffer has 

 conclusively shown that free oxygen does exist in the cell-sap § in the 

 normal condition. 



The importance of this matter for my purpose is that the move- 



G-esell.,' 1888, p. 141). Bokorny ('Ber. d. Deutsch. Bot. Gesellsch.,' 1888, p. 116), 

 who confirmed the above and proved the same for methylal, methyl alcohol, glycol, 

 &c. ; and Saposchnikoff (' Ber. d. Deutsch. Bot. G-esell.,' 1889, p. 258). The organic 

 acids cannot be employed with the same results (see Wehmer, op. cit., p. 713), though 

 they can be absorbed and oxidised in the living cells (Warburg, op. cit., pp. 112 — 

 113) more rapidly than they are decomposed outside the plant. 



* See Schimper, " [Inters, uber die Entstehung der Starkekcrner " ( c Bot. Zeitg.,' 

 1881, p. 881) ; A. Meyer (' Bot. Zeitg.,' 1880, Nos. 51 and 52). 



f For the general exposition, see Sachs, ' Lectures on Physiology of Plants,' 

 pp. 246 — 254, and the text-books quoted. Then Kohl, 'Die Transpiration der 

 Pflanzen,' &c, Brunswick, 1886 ; Eberdt, ' Die Transpiration d. Pflanzen und ihre 

 Abhangigkeit von ausseren Bedingungen,' Marburg, 1889. The literature is col- 

 lected by Burgerstein in ' Verhandl. d. K.K. Zool.-Bot. Gesell. zu Wien,' vol. 37, 

 1887 ; vol. 39, 1889. 



X See G-odlewski's explanation of the fine air-passages which run between the 

 medullary ray-cells and place them in communication with lenticels (Pringsheim's 

 ' Jahrb. f. wiss. Bot.,' 1884, pp. 569—630). 



§ ' Unters. a. d. Bot. Inst, in Tubingen,' vol. 1, p. 684, and " Beitr. zur Kenntniss 

 der Oxydationsvorgar ge in lebenden Zellen " ('Abhandl. der Kgl. Sachsisehen 

 G-esell. d. Wiss.,' vol. 15, 1889, p. 449). 



