DETERRENT TREES AND PLANTS. 27 



Prout at Freetown, Sierra Leone, and was published by Sir William 

 Thistleton-Dyer in the London Times for July 27, 1903, and in 

 Nature, July 30, 1903. Doctor Front's report included an account of 

 experiments made with the ''basil" plant in relation to its effect upon 

 mosquitoes, and he concludes that his observations ''appear to dis- 

 pose conclusivel}^ of the plants possessing an}^ real protective value." 

 He showed that growing plants have little or no effect in driving 

 away mosquitoes, and are not to be relied upon as a substitute for the 

 mosquito net. He showed, further, that fresh ' ' basil " leaves have no 

 prejudicial effect upon mosquitoes when placed in close contact w^ith 

 them, and, further, that while the fumes of burnt "basil" leaves have 

 a stupefying and eventually a destructive effect on mosquitoes, it is 

 necessary, in order to produce this effect, to bring about a saturation 

 of the air which renders it impossible for individuals to remain in the 

 room. He thinks that cones made of powdered ''basil" would, 

 when burned, have the effect of driving mosquitoes away, and that 

 the plant to that extent might be found useful. 



PEAT. 



An article in the London Times in 1908, written by an anonymous 

 correspondent, refers to the absence of mosquitoes in swamps and 

 marshes with peat. The writer says: "Given marshy lands and no 

 peat, mosquitoes abound; given marshy land and peat, there are 

 none." This'article was answ^ered by Mr. F. V. Theobald in Nature, 

 October 15, 1908, pages 607-608. Mr. Theobald showed that he had 

 found Anopheles nigripes and Anopheles hifurcatus breeding in the 

 water of peat cuttings in Wales and Somerset and on the far-famed 

 Wicken Fen numbers of Aedes cantans. He stated that mosquitoes 

 are often very abundant in the fens, even where the peat is dug. 

 Besides the species above mentioned he has found Anopheles maculi- 

 pennis and Culiseta annulata in peaty water and near peat piles in 

 northern Wales. 



WATER PLANTS. 



Ordinary pools of stagnant water give birth to thousands of mos- 

 quitoes, the larvae breeding with the greatest facility in such water. 

 The presence of algae and certain low forms of aquatic vegetation is 

 evidence of the stagnation of the water, and an algal scum is fre- 

 quently associated with the idea of mosquitoes in one's mind. But 

 it is perfectly plain that where the water covering of aquatic vegeta- 

 tion becomes extremely dense mosquitoes can not breed, since there 

 is no opportunity for the larvae to come to the surface to breathe. 

 Access to air is shut off by the dense covering of vegetation. It has 

 often been a matter of surprise that mosquitoes are not more numer- 

 ous in Holland, where the country is traversed by canals and dikes. 



