202 Movement of Water in a Robinia. 



potassium chloride will exert a most beneficial effect in the 

 peach . it is comparatively worthless when applied to the pear, for 

 which the potassium sulphate appears to be the most efficient 

 combination. 



II. Notes on Movement of Water in "Kobinia 



PSEUDACACIA." * 

 By Miss G. E. Cooley. 



The influence of transpiration in determining the upward 

 movement of water in plants is fully recognized ; but, apart from 

 that force, another appears to act in conducting water to the 

 leaves, the proper physical causes of which are not well understood 

 as yet. 



The root-hairs and other active cells of the root derive moisture 

 from the soil through osmosis, and are thus brought into a state 

 of positive tension, while the contained fluid is in a state of negative 

 tension. Sachs*)- points out that the necessary release from this ten- 

 sion must be into adjoining cells as offering the least resistance. 

 These are in turn made tense, and the action continues from the 

 lower to the higher cells, thus conducting the water from the root 

 to the stem. Root-pressure is the expression of this tension of 

 tissues by which water ascends in plants, through osmosis acting 

 as a primary influence. This force of root-pressure is very 

 variable in plants of different species, but in general it is 

 found in all plants with a well-developed root-system. That 

 it is a strong and well-marked force can be readily shown, 

 if the proper conditions are observed, by manometric measure- 

 ments, when the amount is found to be considerable ; as demon- 

 strated by Clark J in the case of Betula lenta, amounting to the 

 equivalent of 68 inches of mercury or 77 feet of water, and of 

 Vitis aestivalis, 78 inches of mercury or 88.4 feet of water. 



Such a power, as this can be shown to be in actively-absorbing 

 roots, must be an important factor in supplying the deficiency of 

 water lost by transpiration ; or, as often happens in some species 



* Observations made in the laboratory of Prof. Penhallow, Mont- 

 real, during the summer of 1885. 

 + Sachs' Text Book, p. 687. 

 t Phenomena of Plant Life, 1874. 



