CHAPTER XIX. 



SYMPTOMS OF DISEASE. 



Discolorations Pallor Etiolation Laying of Wheat 

 Chlorosis Yellotving Albinism Variegation Up- 

 r 00 ting, Exposure a fid Wilting of seedlings. 



Everybody knows in a general way when the 

 geraniums in the window pots are drooping from 

 want of water, or when the young Wheat is sickly, 

 or the Pear-trees " bHghted," and we have now to 

 see how far we can systematise the knowledge that 

 has been gained in course of time regarding the 

 signs which sick plants exhibit. 



Pallor. Under this heading, which includes all 

 cases where the normal healthy green colour is 

 replaced by a general sickly yellow or pale hue, 

 ultimately resulting in death of the parts if not 

 arrested, we have several totally distinct diseases 

 of the chlorophyll apparatus, each recognised by the 

 co-existence of other subordinate symptoms. The 

 principal varieties of pallor usually met with are 



the following 



1/9 



