PLANT DISEASE 



group of symptoms, " which," says Rind- 

 fleisch, " recur with the uniformity of a type 

 in the most various diseases, depending as they 

 do upon one constant factor " (Encyclopaedia 

 Britannica, under " Pathology," vol. xviii. 

 p. 361). 



Now if we return for a moment to chlorophyll, 

 we find another factor of great importance, 

 namely, that " In green plants it is only those 

 cells which contain chlorophyll that can absorb 

 carbon dioxide, and this only under the influence 

 of light, a sufficiently high temperature and a 

 supply of iron " (Encyclopaedia Britannica, 

 vol. xix. pp. 48 and 52). 



Hence green plants deficient in chlorophyll 

 will be deficient in carbon dioxide ; in other 

 words, chlorotic plants are wanting in carbon 

 as well as in iron, because all carbon compounds, 

 whether in plants or animals, are derived 

 directly or indirectly from the organs contain- 

 ing chlorophyll. 



Another important feature which, though 

 not fully recognized to-day, will, I think, be in 

 the near future, and on which I give some 



