628 



which have been robbed of their protective surroundings ; they thereby cool 

 more quickly, thus increasing the danger of dryingV 



The importance of leaving the dead litter of the plants (leaves, bunches 

 of grass, flower stalks of the past year and the like) on seed beds and 

 bushes until late spring is not sufficiently appreciated. Not only is their 

 effect as a protection against frost concerned here, hut also as a protection 

 against the drying spring winds. Almost every year we make the discovery 

 that plants have come well through a severe winter and evergreens have 

 retained their leaves, but if windy, dry weather sets in a few days after the 

 snow has melted, the leavjes, which had remained juicy, dry up. It is 

 possible that, with this rapid drying of the tissues, a similar change may 

 take place in the protein of the protoplasma; Gorke^ proved this recently 

 to be due to frost action. The result in many plants is a complete case of 

 leaf casting disease, which is absent where protection has been afforded by 

 the litter of the previous year. Often our most common perennial blos- 

 soming bushes, grain seeds, tree seeds, etc., are not destroyed until dried 

 in the spring. 



d. Smudge.. 



All these preventative methods may not be used universally in agricul- 

 ture, but the use of smudges which Mayer^ has rescued from oblivion, may 

 deserve still more consideration from the agriculturalist. It was previ- 

 ously repeatedly recommended by Goppert* and Meyen^ and supported by 

 experiments. Fires which develop a good deal of smoke are ignited on 

 the pieces of ground where injury from frost is feared. This process, 

 which, according to Boussingault, had been largely used by the old Incas 

 in upper Peru and is said to have repeatedly found extensive use among 

 the older peoples, is now used again as a protection in vineyards. Accord- 

 ing to Goppert, Olivier de Serres in 1639 and later Peter Hogstrom in 

 1757 endeavored to determine experimentally the effectiveness of the pro- 

 cess. In Wiirtemburg as early as in 1796 and in Wiirzburg in 1803, regu- 

 lations existed, according to which in the autumn, when danger from frost 

 occurred, growers were obliged to light smudges for the vineyards. In 

 Griinberg, Silicia, this method was used for a long time, but it was given up 



1 Kosaroff, P., Einfluss verschiedener ausserer Faktoren auf die "Wasserauf- 

 nahme der Pflanzen; cit. Just's Jahresbericht 1897, I, p. 75. 



2 Gorke, H., tiber chemische Vorgang-e beim Erfrieren der Pflanzen. Land- 

 wirtschaftliche Versuchsstationen L,VX, 1906, p. 149; cit. Bot. Centralbl. 1907. 

 Vol. 104, p. 358. The author explains the cause of death from cold as follows: 

 The sap gradually becomes such a concentrated solution, due to the oliniination of 

 water from the cell, in the form of ice. that a precipitation of the soluBle protein 

 bodies takes place. He bases his theory on experiments with juices extracted 

 from healthy and frozen plant parts. Fresh vegetable sap contained considerablv 

 more water soluble pi'otein than that which had been frozen. The degree of cold 

 at which a precipitation of the proteins takes place in extracted sap varies greatly 

 in the different plant species. In summer barley and rye it fluctuates between 7 to 

 9 degrees below zero. In winter barley and rye, between 10 to 15 degrees below 

 zero; in the needles of Picea excelsa it reaches 40 degrees below zero. Reactionary 

 changes can also co(iperate in freezing. The phosphoric acid, for example, as an 

 aid, is weaker at higher temperatures, and is stronger when cooled down. 



3 Lehrbuch der Agrikulturchemie 1871, I, p. 382. 



4 Warmeentwicklung 1830, p. 230. 

 6 Pflanzenpathologie 1841, p. 323, 



