23 



placed in a dish absolutely prevented emergence while the 

 check teemed with beetles. It made no difference whether 

 light had access to the jar or not. In large receptacles con- 

 taining 100 seers and more, the effect was not so marked even 

 though emergence was reduced by about three-fourths. To 

 decide in which stage of life of the beetles the mercury acted 

 as a poison, the following experiment was tried. Four lots 

 of seeds one in which the beetles had just laid eggs, second 

 in which the larvae were about half grown, third in which the 

 larvae had pupated, and fourth in which the beetles had 

 emerged, were all exposed to the action of mercury with cor- 

 responding check in each case. It was found that the effect 

 was on eggs in which the protoplasm was apparently dis- 

 integrated and the shells became empty. It is possible that 

 no effect was produced on either the larvae or pupae because 

 these stages are wholly spent inside the seed. A fresh 

 series of experiments was carried out which appears to show 

 that the mercury has no action on the eggs once the larvae 

 are fully formed. Detailed results of these experiments 

 which are of scientific rather than of practical interest will 

 be published elsewhere. For the present it is enough to 

 state that, to preserve small quantities from attack, a little 

 mercury placed in the receptacle which need not be air-tight 

 will be quite effective. The treatment does not affect ger- 

 mination. 



With regard to castor oil, the secret of its undoubted 

 efficacy was not revealed until the investigation had continued 

 for some time and the method of penetration by the larvae 

 was discovered. 



It will have become clear from the method of larval pene- 

 tration described, that the larva would be quite helpless if 

 the eggs were not firmly attached to the seed as its main hold 

 is on the egg shell. Larvae carefully dissected out of the egg 

 shell invariably fail to effect an entry into the seed. Now 

 we find that the smearing of the seeds with oil prevents the 

 close adherence of the egg to the seed. Eggs deposited on 

 seeds so treated fail to assume their normal form, and even 

 if they do hatch, fail to furnish the larva with the support 

 that it requires for boring into the seed. For, immediately 

 it starts the boring, the egg shell begins to move. 



Observations on the effect of castor oil when smeared 

 on the upper surface led to the discovery of the instinct of 

 the beetles to seek the top surface. As has already been 

 stated, there was hardly any emergence in seeds which had 

 the top layer treated with the oil. In this case the beetles 



