IX PESTS 159 



the leaves, checks the transpiration or breathing, and 

 lowers more and more, as it increases, the vitality of 

 the plants and the consequent spread of the roots. I 

 gather from Mr. Cranston's book on Rose ciiltm-e, 

 the first edition of which was published in 1855, that 

 it was not so prevalent at that time as it has since 

 become. The greatly increased culture, and the intro- 

 duction of varieties of weak constitution with soft 

 spongy leaves, have probably been responsible for this. 



It is an error to suppose that stout thick leaves are 

 proof against mildew : if soft and succulent these are 

 often the earliest attacked. It is the hard shiny well- 

 glazed leaves upon which the mildew spores can find 

 no footing ; and Teas, whose leaves are rather more 

 of this character, do not generally suffer much from 

 mildew, except under glass, till late in the season. 



Few indeed are the collections of Roses which now 

 pass through a season without at least traces of this 

 pest, though close and confined situations always suffer 

 more than those which are open and exposed to free 

 currents of the air. The amount of harm done will 

 greatly depend upon the time when the mildew first 

 makes its appearance. It is a bad look out to see the 

 first plague spots in June, for if war is to be waged it 

 must be unceasing, as the enemy will constantly reappear 

 when it has once shown itself When well into July 

 the buds will probably be sufficiently advanced to escape 

 serious damage in themselves. 



The life-history of the fungus, called O'idmm leucoco- 

 niuvi in its summer and Sphcerotheca ]_mnnosa in its 

 winter condition, has been thoroughly investigated, a 

 full and interesting paper on the subject having been 

 published in the Bosarians Year Booh for 1886, by 

 Mr. Worthington G. Smith. 



