131 



and this is undoubtedly a fact, and traceable, we pre- 

 sume, to a cessation of the growing principle ; caus- 

 ing, thereby, a concentration of the energies of the 

 plant. We would say, therefore, beware of too high 

 a temperature during the colouring process, unless 

 accompanied with much solar light, and even then 

 avoid extremes. We would more especially avoid 

 night heat at this period, and would promote a circu- 

 lation of air night and day. 



Warts, or Blisters, on the leaves, occur to the 

 cells of the under surface, immediately beneath the 

 cuticle, which become much elongated and multiplied, 

 with a vertical arrangement, the cuticle being some- 

 times wholly, sometimes only partially, obliterated. 

 The leaf is discoloured and withered in consequence 

 of the absorption of the neighbouring chlorophyll 

 by the diseased and multiplied cells. It is very diffi- 

 cult, in the present state of our knowledge of the dis- 

 eases of plants, to say what is the cause, and conse- 

 quently to assign a remedy. Though so strongly 

 resembling one of the epiphyllous fungi outwardly, it 

 is of an entirely different nature. (Gard. Chron. 

 1844, 320.) 



The probable cause seems to be excessive mois- 

 ture to the root, which induces a large supply of 

 sap to the leaves faster than they can dispose of 

 its moisture by transpiration ; ruptures of the ves- 

 sels, and contortions of the parenchyma, are the con- 

 k 2 



