404 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and there seems little doubt that the protoplasm is affected in a similar 

 way to the soluble proteids. Thus death from cold would appear to be 

 due to the alteration of the proteids due to the concentration of salts in 

 the sap, the result of the withdrawal of water into the intercellular 

 spaces. 



It may be pointed out, before leaving this part of the subject, that 

 the death of plants may be due to the drying process brought about in 

 a slightly different way. Strong winds or bright sun acting on foliage 

 of plants in a frozen soil causes them to lose water which cannot be 

 replaced, since the soil is to all intents and purposes dry — the plants 

 cannot get the water locked up in it. 



Lidforss has studied the plants which in Sweden retain green foliage 

 the winter through, and though he finds in the plants no structural 

 protective devices against cold, yet there is one characteristic possessed 

 by all, viz. that while their leaves in summer contain abundant starch, 

 in cold weather this is replaced by sugar and sometimes by oil, which 

 in spring is reconverted into sugar. He showed that the leaves of 

 Oleander when saturated with a sugar solution did not suffer at tem- 

 peratures which were fatal to the normal leaves, thus proving that the 

 presence of much sugar in the sap was a protection to the plant. 

 Lidforss' work affords an explanation to a number of apparently curious 

 facts, such as frost-injury being more severe on the sunny side of trees, 

 the greater amount of injury following a frost succeeding bright warm 

 weather, and so, therefore, brings into line a number of apparently 

 isolated effects, as a true theory should. 



The effect of the presence of sugar would be to retard the freezing, 

 but particularly to check the precipitation of the proteids to which Gorke 

 attributes death through cold — and this effect has been experimentally 

 demonstrated. 



There ar/^ instances of sugar-containing plants which fall easy 

 victims to cold, such as the beet, and, therefore, if the theory pro- 

 pounded by Lidforss be the true one, we are again forced to the conclu- 

 sion that cold-resistance depends not only on the power of the plant to 

 produce such protective substances as sugar and oil in its cells, but 

 upon the specific constitution of the protoplasm itself. • 



[The full returns made, upon which this report is based, are being 

 preserved, and it is hoped that Fellows will, as opportunity occurs, 

 inform us of the behaviour of newly introduced plants under trying 

 circumstances, so that the records may be kept up-to-date. — F. J. C] 



