100 LECTURE VI. 



roots of plants with a solution of a salt of lithium, and deter- 

 mining, by means of the spectroscope, the length of stem in 

 which lithium could be detected after the lapse of a given 

 time. The following are some of the results which he obtained, 

 the plants being under such conditions as to promote their 

 transpiration as much as possible. 



Plants with roots in water Rate of rise per hour 



Salix fragilis 85-0 cm. 



Zea Mais ... ... ... 36*0 



Plants with roots in earth 



Nicotiana Tabacum 118*0 



Albizzia Lophantha I54'o 



Musa Sapientum ... ... 99^7 



Helianthus annuus 63*0 



Vitis vim/era 98*0 



It must be pointed out that Sachs ascertained by means of experi- 

 ments with strips of blotting paper, that the lithium salt travels as 

 rapidly as the water in which it is dissolved : but it does not necessarily 

 follow that this is the case in the plant. 



It is, then, by means of the fibro-vascular tissue that water 

 is distributed to all parts of the plant, and, provided that the 

 supply absorbed by the root is adequate, with sufficient rapidity 

 to maintain the turgidity even of those parts in which trans- 

 piration is active. The distribution of water from the fibro- 

 vascular bundle in a transpiring organ, a leaf for instance, 

 follows a course which is the exact converse of that which 

 takes place in the root. In this case the more external cells, 

 those which bound the intercellular spaces, are those which 

 are first affected by transpiration ; they obtain fresh sup- 

 plies of water by osmosis from the more internal cells, and 

 these, in turn, obtain water from the cells of fibro-vascular 

 bundles with which they are in relation. There is thus a 

 current of water set up passing from within outwards. 



We became acquainted at the outset with the remarkable 

 property possessed by the parenchymatous cells of the roots 

 of absorbing water to such an extent as to set up sufficient 

 pressure to cause water to filter out of them. This property 

 is, however, not peculiar to the cells in question, and we may, 

 in concluding this lecture, briefly consider the instances which 



