Dixon and Atkins — On Osmotic Pressure in Plants, Sfc. 305 



some 10 e.c. of sap were pressed immediately, and divided into three parts. 

 The first was examined immediately. The second was filtered, stored till 

 next day, and then tested. The third was stored unfiltered, and tested next 

 day. Lot b was stored in the dark till next day, when it was pressed and 

 examined. 



Table XXII. 



Syringa vulgaris : leaves. 



The rise in mean molecular weight, in Nos. 74 and 72 is small, and if 

 of any significance, again indicates the production of maltose from starch, 

 which must have been present in tlie uninjured cells and in the unfiltered sap. 

 At the same time respiration in tlie uninjured cells, we may assume, reduced 

 the amount of dextrose, and so prevented a rise in osmotic pressure. In 

 No 73 — the filtered sap — the pressure rose owing possibly to the inver.sion 

 of cane-sugar to dextrose and levulose. The same process woidd cause a 

 sliglit fall in molecular weight. The solid matter having been removed, 

 no maltose could be formed, and so no rise of mean molecular weight from 

 this cause was to be expected. In 74 there is tlie same cause for a rise in 

 osmotic pressure as in 73, and the same reason for increased mean molecular 

 weight as for 72. 



Whatever is the cause of the alteration in the osmotic pressure of tlie sap 

 on keeping, its amount, wliich in no ease exceeded \7 atmospheres, is quite 

 unable to obscure the effects of assimilation and evaporation, which have 

 been observed to cause changes of pressure amounting to as mucli as eight 

 atmospheres. 



It is interesting to find that these results are quite justified by Brown 

 and Morris's analyses' of the sugars of leaves, and investigation of tlie 

 change in them on keeping. Tliese authors give, in their memoir on tlie 



' Brown and Morris, Chemistry and Pliysiology of Foliage Leaves : Journ. Chemicid Soc, ifay, 



