14 BULLETIN 938, U. S. DEPARTMENT OF AGRICULTURE. 



petioles of the leaves were left projecting above the surfaces of the 

 solution. An hour later the four treated leaves vrere put into absolute 

 alcohol and a day later a few of the stained leaves on the tree were 

 likewise treated. The absolute alcohol did not dissolve or scatter 

 either one of the stains, and the only other reagents used were xylol 

 and Canada balsam ; these also did not scatter the stains. A study of 

 the sections made shows much stain on the outside of the sprayed 

 and submerged leaves. While none was observed inside the sprayed 

 leaves, it was usually present inside the submerged ones and the most 

 of it seems to have passed through the ventral surfaces of the leaves. 

 Its passage may have been aided by the stomata which occur exclu- 

 sively on the ventral surface of these leaves ; botanists, however, say 

 that the stomata are so small (0.0006 mm. and less) that neither dust 

 nor water can pass through them into the plant. According to the 

 above results the spray solutions did not pass into the leaves sprayed. 

 nor did the dust in the film of adhering nicotine sulphate enter the 

 stomata. 



SUMMARY OF EXPERIMENTS CONDUCTED IN LABORATORY. 



Nicotine sulphate as an ovicide, with one exception, was found 

 inefficient against all of the eggs tested — namely, those of the silk- 

 worm moth, codling moth, tussock moth, and potato beetle. The 

 eggs sprayed with it were variously affected, depending on the 

 strength of the spray solution used, on the age of the eggs tested, 

 and whether or not the solution contained soap. Upon the eggs of 

 three of the species of insects used there was practically no differ- 

 ence in effects between solutions containing soap and those without 

 soap, although those with soap were much more effective upon the 

 eggs of the tussock moth. Comparing the effects of the spray solu- 

 tion 1 : 800, the strongest one of the economic solutions used, the 

 percentages of eggs sprayed with it that failed to hatch are as fol- 

 lows : Xinety-nine per cent of the freshly laid eggs of the silkworm 

 moth, but only about 75 per cent of the older eggs of the same- 

 insect ; about 20 per cent of the codling-moth eggs on apple-tree 

 foliage; 75 per cent of the tussock-moth eggs (1 to 3 days old) : and 

 about 12 per cent of those of the same insect which had been col- 

 lected in the field ; and practically none of the potato-beetle eggs. 



The effects of the exhalation from leaves sprayed with solutions 

 of nicotine sulphate varied considerably, depending on the larva? 

 tested and the strength of the solutions used. Again comparing the 

 effects of the solution 1 : 800, all of the newly hatched silkworms and 

 codling-moth larva? placed upon leaves sprayed two hours previously 

 died, but the silkworms succumbed the more quickly; all of the silk- 

 worms but only a small percentage of the codling-moth larva? placed 

 upon leaves sprayed 24 hours previously died. 



