Dixon and Atkins — Osmotic Pressures in Plants. 



387 



Ilex aquifolium, 3 ft. 

 Populus alba, 40 ft. 

 Saliw babylonica, 18 ft. 



Concentration at different Levels. 

 The pieces of the stems yielding the sap examined in these experiments 

 were always taken from the same plant and from the same level. These 

 levels above the ground were as follows : — 

 Acer pseudoplatanus, 25 ft. 

 Cotoneaster frigida, 20 ft. 

 Fagus silvatica, 40 ft. 



It seemed desirable to compare the sap from the same level on the 

 different occasions in case a difference in level in the tree is associated with 

 a change in concentration.' 



This point was also separately investigated for one tree, viz., Acer 

 macrophyllum (see Table X). 



The subject for the investigation was an old tree which had been cut 

 across near the ground many years previously. From the level of the soil 

 three similar branches about 30 cm. in diameter took their origin, and rose to 

 a height of about 10 m. One of tliese was cut down in the middle of 

 October, and samples of the wood excised at various levels, viz.: (1) ground- 

 level, at (2) 2 metres, (3) 4 metres, (^4) 6 metres, and at (5) 8 metres above 

 ground-level, and finally (6) from the small branches about 10 metres above 

 the ground. The following table gives the results of determinations made 

 on the sap centrifuged from the wood at these levels, and shows how the 

 concentration varies from below upwards at that time of year : — 



Table X. 

 Acer macrophyllum, Wood-sap, October. 



^ Schroder (10) found this to be the case in bleeding- sap Qi Acer platanoides and Betula. The 

 sugar concentration in Acer was found to be greater in the root and in the upper parts of the stem 

 than in the lower parts of the stem. In Betula, on the contrary, the concentration of the bleeding 

 sap is less above in the stem and in the root than it is in the base of the stem. 



