149 



the protoplasm of the plant is directly susceptible to cold and that 

 each cell has a fatal minimum temperature. 



Gorke showed that freezing causes a precipitation of some of 

 the soluble proteids and that the temperature required for this 

 purpose varies widely with different species of plants. 



Lidforss has recently found an agency in plants that protects 

 them against cold. 



He finds that all winter-green leaves are quite free from starch 

 but contain sugar and oil in the mesophyll; in the summer these 

 same leaves contain abundant starch. Tbe only exception found 

 by him was in submerged plants which show starch throughout 

 the winter. 



The sugar in the cells aids in keeping down transpiration and 

 enables the plants to withstand lowered temperatures. 



The frequent killing of trees early in the spring, is held to be 

 due to the regeneration of starch, making the plants more suscep- 

 tible to sudden cold. 



The occurrence of sugar and oil in winter in the periderm of 

 tree trunks has also been reported. 



Protection of Fruit against Frost by Smudging. (four, of 

 South- Eastern Agric. Coll., No. 17, 1908). The four, of the Board 

 of Agric., March 1910, London, vol. XVI, No. 12. p. 1024. 



" Owing to the absence of severe frosts it was impossible to 

 test the effect of smudging, but some progress was made in discover- 

 ing that the best method employed was that of making a hot black 

 smoke by burning a mixture of naphthalene and creosote in the 

 iron pots recommended in an article in the fournal of the Board 

 of Agriculture, April 1907, p. 23, forty pots being used to the acre. 



It was found that lighting up forty pots took one man about 

 twenty minutes. If the pots are lit up early, as appears to be 

 necessary, and the frost continues till sunrise, it is necessary to 

 relight them, and the refilling and relighting of forty pots took three 

 men a considerable time. 



The dense black smoke did not scorch the bushes, but those 

 near the pots were covered with black smuts. These washed oft 

 after a few days' rain, but smudging would be impracticable if early 

 rhubarb or other low-growing plants and vegetables nearly ready 

 for market were grown between the rows, or where the plantation 

 is close to houses. The cost, including labour, five_ acres being 

 done at a time, is estimated at 25^. ^d. per acre. If a refill is 

 necessary, the cost would be about 22.?. more." 



