Dixon and Atkins — Osmotic Pressures in Plants. 



61 



Table XII. 

 Ilex aquifolium, March 22nd. 



While obtaining the sap for these determinations one could not help 

 heing struck by the surprising amount which may often be extracted from 

 fresh wood by centrifuging ; thus the wood of Salix babylonica cut in 

 December gave as much as 4 c.c. from a cylinder about 2 cm. diam. and 

 10 cm. long ; and a similar piece of the root of Cotoneaster frigida yielded 

 almost as much in the month of February. A yield of 1 - 2 - 5 c.c. was the 

 usual quantity from pieces of wood of this size. Similar cylinders (viz. 2 cm. 

 diam., 10 cm. long) of Hex aquifolium seldom yielded as much as 1 c.c. 



The differences in the colour of the sap are also remarkable ; some are 

 pale brown, e.g. that from Acer macrophyllum, A. pseudoplatanus, Populus 

 alba, Cotoneaster frigida, and Ilex aquifolium (the last often inclines to grey) ; 

 others, e.g. from Fagus silvatica and Salix babylonica, are of a wonderfully 

 beautiful amethystine hue. The presence of oxidases is often indicated by 

 the darkening of the sap on exposure to air. It is open to question how far 

 these pigments and oxidases are derived from the injured cells of the wood 

 centrifuged, and how far they are to be regarded as part of the constituents 

 of the transpiration stream in the uninjured stems. 



Summary. 



1. Large quantities of sap may, as a rule, be centrifuged from the 

 conducting wood of trees. This sap varies in colour and in electrolyte and 

 non-electrolyte content. 



2. When in a condition of physiological rest during the late autumn and 

 winter, the osmotic pressure of the wood-sap of deciduous trees is small and 

 approximately constant throughout ; the stems, the roots, and upper portions 



