PLANT DISEASES 



INTRODUCTION ' 



The knowledge necessary to enable the horticulturalist, 

 farmer, or forester to utilise to the fullest extent the 

 discoveries of specialists relating to plant diseases, and 

 also to convey to others an intelligible account of the 

 particular form of disease respecting which information 

 is desired, may be arranged under three sections, as 

 follows : — 



I. Familiarity with the general appearance and name 

 of the most frequent groups of parasites; their varied 

 modes of attack, and the special conditions favouring the 

 same ; also the relationship between the different forms 

 assumed by certain parasites during different periods of 

 their existence. 



This last item. of knowledge would, in one instance, have 

 saved from destruction a quantity of valuable young 

 standard pear-trees that were attacked by the pear leaf 

 cluster-cup fungus {Gymnosporangium sabinae). These trees 

 were cut down for the avowed purpose of preventing the 

 spread of the disease ; at the same time the solitary juniper 

 plant {Juniperus sabinae), the real cause of the mischief, 

 was, through lack of knowledge, allowed to stand. 



II. Preventive Measures. — The old maxim, ' Preven- 

 tion is better than cure,' embodies the keynote to success 



A 



