INTUMESCENCES AND WARTS 43 



but is not common, and must not be confounded with the 

 excessive growth which gives a rugged appearance to stems, 

 as in Acer campestre, the lower portion of the stem of Lythrum 

 when growing in water, etc., although the latter examples may 

 probably be the outcome of causes similar to those grown in 

 houses, which in both instances consists in the formation of a 

 mass of suberised or corky tissue composed of very large, 

 thin-walled cells containing air. In the case of plants grown 

 in warm houses, it is known that ' sap-warting ' is favoured by 

 an excess of heat and moisture, and is quite independent of 

 the influence exercised by fungi or insects. In some cases, as 

 in acacias, a certain amount of gum is produced, due to the 

 breaking up of cells in the ruptures ; this gum serves as a 

 starting-point for the development of species of Botrytis, 

 Cladosporium, and other minute fungi, whose mycelium 

 eventually passes into the injured tissue, and sometimes also 

 extends to the surrounding living tissue. Such fungi often 

 intensify the original injury, but being in all instances wound- 

 parasites and incapable of penetrating an unbroken surface, 

 cannot be considered as the primary source of mischief. 



Practically I have repeatedly noted that good ventilation, 

 especially when applied in the morning, along with a reduction 

 of temperature, checked the formation of warts on vine leaves. 

 Such disfigured leaves are being constantly submitted for 

 examination, with a query as to whether the warts indicate the 

 presence of Phylloxera, the general appearance being the 

 same in the two diseases. 



Sap-warting yields also to the treatment indicated above. 



Schrenk has recently described the formation of small warts 

 on the under surface of cauliflower leaves, that had been 

 sprayed with a copper and ammonium carbonate solution to 

 check the progress of Peronospora parasitica. Various other 

 copper sprays were also used, to which a small quantity of 

 fish-glue was added to cause the spray to adhere more firmly 

 to the leaves. In all cases the warts appeared a few days 

 after spraying. Numerous experiments were subsequently 

 made with sprays of different kinds on cauliflowers, and also 

 with the various components of the solutions used separately. 

 The following is Schrenk's summary. 



1. Cauliflower plants sprayed with copper ammonium 

 carbonate (5 oz. copper carbonate, dissolved in a mixture of 

 3 pints ammonia to 50 gallons of water) produced large 

 numbers of intumescences as a direct result of the spraying. 



