202 BACTERIA IN RELATION TO PLANT DISEASES. 



The stage at which cold water should be poured on to stop the cooking varies with different 

 limes. Some limes are so sluggish in slaking that it is difficult to obtain enough heat from them to 

 cook the mixture at all ; while other limes become intensely hot on slaking and care must be taken 

 not to allow the boiling to proceed too far. If the mixture is allowed to remain hot fifteen or 

 twenty minutes after the slaking is completed, the sulphur gradually goes into solution, combining 

 with the lime to form sulphides which are injurious to peach foliage. It is therefore very impor- 

 tant, especially with hot lime, to cool the mixture quickly by adding a few buckets of water as soon 

 as the lumps of lime have slaked down. The intense heat, violent boiling and constant stirring 

 result in a uniform mixture of finely divided sulphur and lime with only a very small per cent 

 of the sulphur in solution. The mixture should be strained to take out the coarse particles of lime, 

 but the sulphur should be carefully worked through the strainer. (From Scott and Ayres' Bulletin 

 on The Control of Peach Brown-Rot and Scab.) 



Alsberg and Hasselbring in U. S. Department of Agriculture in the summer of 1909 

 .subjected cabbage leaves to i :2oo mercuric chloride water for 30 minutes without entirely 

 sterilizing their surfaces, i.e., a white schizomycete subsequently appeared in the flasks con- 

 taining the leaves which were to have been examined chemically. In this instance, however, 

 the leaves were rather large and were not previously soaked in alcohol. 



INSECTICIDES. 



Carbon bisulphide is an excellent insecticide for certain purposes. Its vapor is inflam- 

 mable and care should be exercised in its use. It must not be used near an open flame. 



In 1897, Hicks and Dabney showed that there was no appreciable loss of germinating 

 power in wheat, corn, barley, or rye, from treating the seed in bulk with carbon bisulphide 

 for 24 hours at the rate of one pound of the chemical to 100 bushels of grain. 



In recent years it has come to be recognized that carbon bisulphide is better adapted 

 to kill certain insects, e.g., weevils in grain, phylloxera in the soil, etc., than hydrocyanic 

 acid gas, because it has greater penetrating power. One teaspoonful per cubic foot is the 

 usual amount allowed in making small treatments (Jno. B. Smith). 



For aphides on plants in the open air, kerosene emulsion is useful. To make it one 

 must have a force pump with good churning power. When properly made it may be kept 

 for some weeks and diluted with water as needed for spra)dng. 



For aphides in houses tobacco smoke properly applied is very effective and not injurious 

 to the plants. Improperly applied, it may burn the foliage seriously. The houses should 

 be well wet down in advance, and then a prepared tobacco paper burned until there is a 

 dense smudge, or else the house filled with the steam from strong tobacco water. This 

 latter may be obtained by distributing shallow pans of the concentrated fluid at frequent 

 intervals and dropping large red hot spikes into the liquid from a wire crate which has 

 been heated in the engine-room furnace. It may also be evaporated from pans placed 

 over oil stoves. This concentrated tobacco extract may be had on the market under the 

 name of Nicofume. 



Aphides and most other pests in houses may be destroyed by hydrocyanic acid gas. 

 This treatment is inexpensive and very effective. Only red spiders do not seem to be much 

 harmed by it at least in such doses as can be used on plants. Plants are also sensitive to 

 this poison but to a less degree than most animals. Different varieties of plants also vary 

 considerably in sensitiveness. The tomato and olive are quite sensitive. The aim of the 

 grower should be to generate just enough of the gas per cubic foot to destroy the insects 

 without injuring the plants. If the grower has no knowledge of the amount of gas which 

 his crop will tolerate, then he must determine this on a small scale before applying the 

 remedy to a whole house, otherwise disastrous results are likely to follow. 



Eggs of insects, e. g., those of the white fly {Aleyrodes), are more resistant to this gas 

 than the mature forms, or the plants infested, and therefore small doses of the gas at 



