ROOT CROPS. 57 



method of utilizing the sulphate is to prepare a solution 

 containing from 1 to 5 per cent, of commercial iron 

 sulphate, and distribute it by means of a Strawsonizer 

 at the rate of two gallons an acre. M. Delacharlonny 

 (JBiedermann's Centralblatt fiir Agricultur-Chemie, vol. 

 xviii.) has coniirmed the author's investigations, and 

 states that iron sulphate is best applied when the young 

 potato plants have reached the height of a few inches. 

 (2) Top-dress the land (when the plants are a few inches 

 above ground) with ^-cwt. of iron sulphate mixed with 5 

 to 10 times its weight of sand or dry earth per acre. The 

 above dressing destroys the fungus in the early stages of 

 its life-history. (3) M. Prillieux {Comptes Rendus, vol. 

 107, p. 447) has used a mixture containing copper sulphate 

 {blue vitriol) for destroying Peronospora infestans. This 

 mixture is made " by dissolving in every 10 gallons of 

 water 6 lbs. of copper sulphate, and then adding 6 lbs. of 

 slaked lime." Dr. J. M. H. Munro {Bell's Weekly Mes- 

 senger, Feb. 4th, 1889) recommends the above mixture to 

 be applied by means of the Strawsonizer or pneumatic 

 distributor. 



The Potato Smut {Tubercinia scabies) is a fungus 

 which confines itself entirely to the tubers of the potato. 

 It lives between the cuticle (" skia ") and the epidermis 

 of the tuber, often causing a dark-brown envelope over 

 the entire potato. This fungus is to be recognised by the 

 discoloured patches on the cuticle of the tubers. The 

 greenish-brown spores of Tubercinia scabies are com- 

 pound, i.e., they are multi-cellular. The cells unite form- 



modificatiori of the cellulose found in the higher plants. Hence the 

 reason of the difference in the action of iron sulphate in the two 

 cases. 



