38 LECTURE III. 



densation, and this has been found to be the case. Reinke 

 ascertained that the thallus of Laminaria absorbed 230 per 

 cent, by weight of water, and that the water underwent a con- 

 densation of O'2 per cent. 



The maximum amount of water which a cell-wall may 

 absorb varies with the constitution of the membrane and jwith 

 various external conditions. Naegeli found that the gelatin- 

 ous cell-walls of Nostocaceae and Palmellacese may contain 

 as much as 200 parts of water to I of solid substance ; on the 

 other hand Sachs has estimated the amount of water which 

 100 c. cm. (156 grm.) of dry wood of Finns sylvestris may 

 take up to be about 50 c. cm. Temperature has an important 

 influence ; the amount of water absorbed in a given time is 

 greater at a higher than at a lower temperature. Further, the 

 presence of a substance in solution in the water may affect 

 absorption. Thus Reinke found that peas placed in distilled 

 water for three hours increased 43*2 per cent, in volume, 

 whereas when placed in a mixture of 100 parts of water and 

 30 of alcohol the gain was only 22*5 per cent: in another 

 experiment some peas placed for 2\ hours in water increased 

 54*5 per cent, in volume, and others in a solution of 20 parts 

 of calcium chloride in 100 of water increased only 19*1 per 

 cent. On the other hand it is well known that the presence 

 of acids or alkalies in the water increases the swelling-up of 

 organised bodies. If, however, the acid or the alkali be 

 present in large proportion so that the solution is tolerably 

 concentrated (and this is also true in many cases of the action 

 of water at a high temperature), the swelling-up becomes ex- 

 cessive, and the body cannot be restored, as it can under 

 ordinary circumstances, to its normal size by washing out the 

 acid or the alkali. Evidently some permanent alteration in 

 its constitution has been effected, for if it be dried, and be 

 then placed in water, it will not again swell up. It has lost 

 the power of absorbing water as well as any special optical 

 properties which it may have possessed. Its organised struc- 

 ture has been destroyed. 



We may note here two facts which will be found useful 

 hereafter in discussing the movement of water in plants. 



