242 CULTURE OF THE GRAPE. 



>with oxygen, forming sulphurous acid in the proportion 

 of one part sulphur and two parts oxygen. Now, when 

 we use dry sulphur, it is converted into a gas so slowly, 

 that the grape-foliage receives no perceptible injury. But 

 the parasitic fungus is far more sensitive, and perishes 

 upon the least perception of this gas. 



And yet, though we express the opinion that the sul- 

 phur acts as a direct poison upon the fungus, and that its 

 chief merit consists in this, still it may be well to consider 

 how far the enfeebled state of the foliage, and of the ber- 

 ries also, in the case of black rot, is caused by a lack of 

 sulphur in the plant, arising from a lack in the soil. If 

 this were true, possibly the slight amount of sulphurous 

 gas given off, instead of being an injury, may be, to some 

 extent, directly inhaled by the leaves in sufficient quantity 

 to give them tone, and enable them better to withstand 

 the attacks of mildew. Careful observation may enable 

 us better to understand the principle upon which sulphur 

 acts. 



It will be obvious, that though this mode of using sul- 

 phur is easy and safe, yet we get but a small percentage 

 of the virtue of the sulphur at the time of application. 

 This involves a loss of material to some extent ; but, on 

 the other hand, there is an advantage in having a pro- 



