18 Dust and its Importance to Plant Life. 



over 90 per cent, seem to make use of the dust which falls upon 

 their foliage. 



As regards mites, I am very far from believing that they do 

 not occur upon a large proportion of those plants upon which 1 

 have not as yet noticed them. It was rather against my plan to 

 examine one plant over and over again, but when I did so it 

 almost always resulted in discovering mites somewhere. This 

 positive evidence seems to me very strongly in favour of the view 

 that mites are excessively common even in temperate countries. 

 One cannot, for instance, deduce from the fact that acarodomatia 

 occur on fossil leaves of the Piedmont tertiary deposits, any con- 

 clusion as to the climate being warmer than that of the same 

 distri.n to-day.* 



So that instead of keeping, as a farmer has to do, expensive 

 herds of Irish cattle that must be fed on dear cake in order to 

 improve his pastures, plants may be said to support great herds of 

 wild yet benevolent mites which feed themselves from the dust 

 which falls upon their leaves, like manna, from the skies. 



It would also be very interesting to know whether nitrate of 

 soda or such like manures might not be applied as dilute solutions 

 by spraying the foliage. It would seem well worth trying experi- 

 ments to test the economy of this method of applying such 

 manures. 



Literature. 



Aitken. Nature, Vol. 41, 1891. 



Annibale. Boll. Soc. Naturalist, Napoli, Vol. 21, 1907. 



Anon. Journ. R. Hort. Society, May, p. 659, 1904. 



Chardot. Comptes Rendus Tome, 142, 1906. 



Cieslar. Centralblatt f. g. ges., Forstwesen, Heft 1, Wien, 19C4. 



Delpino. Boll. Soc. Bot. Ital., 1901. 



Guerin. Bull. Soc. Bot. d. 1. France, Tom. 53, 1906. 



Hall. Rotliamstedt Experiments, London, 1905. 



Hansen. C. B. Bact., Vol. 14, 2nd abt. 1904. See also Jorgensen. 



Henslow. Journ. Linnean Society, 1880, p. 313. 



Jamieson. Agricult. Research Association, Aberdeen, 1906, 1907-8. 



Jorgensen. Micro-organisms and Fermentation. 



Jungner. Zeits. f. Pflanzenkrankheiten, 1904. 



Kerner van Marilaun. Natural History of Plants. 



Klebakn (for Dietel's Experiments). Die. Rostpilze, Berlin, 1904. 



* Peola. 



