192 Physiologie. 



point over this period was 0.799° for the south-aspect leaves and 

 0.748'^ for the north-aspect leaves. indicating osmotic pressures of 

 9.61 atm. and 9 atm. respectively. This result is parallel to Tran- 

 chieri's observ'ations on Salpichroa rhomhoidea, and the higher 

 average cryoscopic value of the insolated leaves finds an obvious 

 expianation in the increased photosynthesis and evaporation. The 

 highest figures for the freezing-point depression in winter coincide 

 with frosty weater, when the raising factors of photosynthesis or 

 Solution or both maj^ have been active, while the cold completely 

 or partially inhibited respiration and translocation from reducing 

 the concentration; apparently this is the only instance of external 

 conditions producing a well-detined effect on the seasonal curve of 

 the cryoscopic values of the sap of Hedera. F. Cavers. 



Dixon, H. H. and W. R. G. Atkins. Variations in the os- 

 motic pressure ofthe sap of Hex Aqiiifolium. (Sei. Proc. Roy. 

 Dublin Soc. XIII. 18. p. 229—238. 1912.) 



Details, with tables and graphs, are given for a large number 

 of determinations of the osmotic pressure of the sap of the leaves 

 and roots of Hex Aquifolimn at different times. The general results 

 are similar to those obtained with Syringa vulgaris. The number 

 and curves given show the somewhat erratic manner in which the 

 freezing-point (and with it the osmotic pressure) of the sap varies. 

 It is noted that intensity of Illumination does not define the rises 

 and falls of the curves; the lowest average pressure was found in 

 the summer months; an attempt to correlate the rainfall with the 

 cryoscopic values gave no definite result. Despite the fluctuations, 

 upon which Illumination and rainfall seem to exercise no direct 

 infiuence, the annual curves show two distinct cusps, one about 

 November or December and the other about March or April, with 

 corresponding depressions, one about February and the other about 

 June or July. These depressions seem to correspond roughly with 

 the ends of the periods of elongation of the growths; in autumn 

 the buds may begin to open in October and the axis may continue 

 to elongate tili January; in spring the leaves begin to unfold in 

 Ma3^ and elongation proceeds tili July or longer. The roots of Hex 

 showed in March the lowest record (3.54 atm.) for any plant exa- 

 mined by the authors; it seems that roots are able to maintain 

 the cryoscopic values of their sap irrespective of large variations 

 in the amount of soil-water. On the other hand the highest mole- 

 cular weight (300) was found in the leaves of Hex in October; the 

 lowest for the leaves of Hex (215) was given in February. 



F. Cavers. 



Keeble, F. and E. F. Armstrong. The distribution ofoxy- 

 dases in plants and their röle in the formation of 

 Pigments. (Proc. Roy. Soc. LXXXV. 578. p. 214—218. 1912.) 



Hitherto the methods of investigation in general use have been 

 inadequate to determine in detail the distribution of oxydases in 

 the tissues of plants and animals. hence the hypothesis that pigments 

 are produced by the action of oxydases on colourless chromogens, 

 though rendered probable by recent researches, could not be regar- 

 ded as established. The authors describe methods which allow of 

 the ready detection, macroscopic and microscopic, of plant oxyda- 



