MOVEMENT OF WATER IN PLANTS, 68 1 



place in a solution of lithium citrate, and then examined the ashes of successive inter- 

 nodes by the spectroscope. The solution was found to rise from 42 to 46 cm. in one 

 hour. But neither method of calculation is exact or probably of much value. 



The current of water in the wood which replaces the loss occasioned in the leaves 

 by transpiration is not caused by osmose, since at the time when the transpiration is 

 strongest and therefore the current in the wood quickest, the cavities of the conducting 

 wood-cells do not contain sap but air, or at the most are only partially filled with fluid. 

 If the rising of the water took place by endosmose from cell to cell, the cells would 

 necessarily possess closed cell-walls and be full of sap, the concentration of which would 

 constantly increase from below upwards in the wood. But the conducting cells are at 

 this time not closed, but partially or altogether (as in Coniferge) connected with one 

 another by open bordered pits ^. In the spring, before strong transpiration sets in, ai;d 

 therefore at a time when the water in the wood is comparatively at rest, the wood-cells 

 also, it is true, contain sap, flowing in quantities out of their communicating cell-cavities 

 when holes are bored in the trunks (as in the Birch, Maple, &c.). But this sap does 

 not, as is proved by analysis ^, show a concentration increasing from below upwards. 

 The fact ^ also that water rises in cut leafy stems placed with their upper end in water 

 though planted and rooted, and flows therefore in a direction opposite to the ordinary 

 one in the stem, shows that endosmose depending on a definite distribution of the 

 concentration of the sap cannot be the cause of the current of water. Since vessels 

 and wood-cells communicating with one another through their open pores form narrow 

 cavities which sometimes become wider as they proceed, sometimes narrower, the woody 

 substance may be represented by a bundle of narrow glass tubes alternately bulging and 

 contracting, in which the water which fills them rises by capillary attraction. But how 

 little efficacious a contrivance of this kind would be is seen at once from the width of 

 the capillary tubes, which is much too great to raise water to a height of 100 feet or 

 more. It must also be pointed out that in the summer, when the current of water 

 is strongest, it is principally air and not fluid that is conveyed through the cavities of 

 the cells. 



Since it is evident from what has been said that the movement of the water takes 

 place in the woody substance and not in the cell-cavities filled with water, there remain 

 only two hypotheses; 'viz. (i) that the movement takes place in the water contained 



Irish Acad. vol. XXV, 1874). Sachs has foxind that salts of lithium do travel along cell-walls as fast 



as the water in which they are dissolved. By supplying the roots of plants with a solution of a salt 



of lithium, he has obtained the following rates at which it travelled in the root and stem : — 



Plants with roots in water. Rate per hour. 



SalixfragiUs .... 85*0 cm. 



Zea Mais . . . , . 36*0 „ 



Plants with roots in earth. 



Nicotiana Tnbacum . . . I180 ,, 



Albizzia lophantha . . , 154'0 >» 



Mtisa Sapientntn .... 99*7 » 



Helianthus annuus . . . . 630 ,, 



Vitis vinifera .... 98'0 „ 



In all these cases the plants were under such conditions as to promote transpiration to the utmost. 



(Sachs, Beitr. z. Kennt. d. aufsteigenden Saftstroms in transpirirenden Pflanzen, Arb. d. hot. Inst, in 



Wurzburg, II. i, 1878.] 



^ [Sachs has found that in Abies pectinata the bordered pits of the spring-wood are closed 

 (Porositat des Holzes).] 



^ The older statements of Unger are referred to in my ' Experimental -Physiologic ; ' others will 

 be found in Schroder, Jahrb. fUr wiss. Bot. vol. VII. p. 266 el seq. 



^ The conduction is however by no means so considerable in the reversed as in the ordinary 

 direction, as Baranetzky found in the laboratory at Wurzburg ; but this may be connected with other 

 peculiarities of the organisation. 



