AQUATIC PLANTS 417 



A number of other plants have been mentioned from time to time in the news- 

 papers, some of them in a sensational manner. The New York papers, for 

 example, in the summer of 1906, contained numerous notices of the so-called 

 Phu-lo plant introduced from the Tonquin country in China by Baron de 

 Taillac. This plant was said to be valuable as a fodder for cattle, and to drive 

 away mosquitoes. An effort was made to determine the plant and Mr. W. B. 

 Safford searched the literature of oriental economic botany without finding any- 

 thing corresponding to it. He found that in the East Indies there is a Ver- 

 bascum or mullein called Phul, the seeds of which are supposed to be narcotic, 

 and the leaves used like those of tobacco. The leaves of this plant, although not 

 good for general forage, are eaten by camels and goats. Assuming that this is 

 the plant mentioned by the newspapers, there is nothing in the economic litera- 

 ture concerning its use as a mosquito deterrent. 



PEAT. 



An article in the London Times in 1908, written by an anonjmaous corre- 

 spondent, 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 answered by Mr. F. V. 

 Theobald in Nature, October 15, 1908, pp. 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 rnaculipennis and Culiseia annulata in peaty water and 

 near peat piles in northern Wales. 



WATER PLANTS. 



Ordinary pools of stagnant water are often the source of thousands of mos- 

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

 persons the presence of algae and certain low forms of aquatic vegetation is 

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

 ciated with the idea of mosquitoes in one's mind. But, it is perfectly plain that 

 where the water covering of aquatic vegetation becomes extremely dense and 

 complete mosquitoes can not breed, since there is no opportunity for the larvae to 

 come to the surface to breathe. It has often been a matter of surprise that 

 mosquitoes are not more numerous in Holland, where the country is traversed 

 by canals and dykes. Mosquitoes breed there, as elsewhere, in ponds and in 

 chance receptacles of water, but it is said that no larvae are present in the water 

 of the canals. It is explained that this is so constantly agitated by the passage 

 of boats and by the wind that mosquitoes can not breed there, and that in the 

 smaller ditches and canals the surface of the water becomes so completely covered 

 vtdth a continuous layer of minute aquatic vegetation early in the summer that 

 there is no opportunity for the extensive breeding of mosquitoes. 



