CHAPTER X 
GENERAL SUMMARY 
WHETZEL in his History of Phytopathology (1918) says that 
‘modern pathologists may be divided, for the most part, 
into two philosophic schools, the pathogenetists and the 
predispositionists’. Most of us object to being labelled, and, 
for our part, we do not call ourselves either pathogenetist 
or predispositionist. Nevertheless the terms have their 
value. Every disease described in this book is caused by 
some specific fungus, and this fungus is considered as the 
primary factor in the etiology of the disease. With some 
of the diseases secondary factors have also to be taken into 
account, such as sylvicultural conditions, which make for 
the good or bad health of the tree as a whole. The patho- 
genetist emphasizes the primary factors, the predispositionist 
the secondary factors. But whether we are to be one or 
the other depends entirely on the disease which we are 
considering. The general health or tone of the tree plays 
no part in the incidence of diseases caused by the rusts 
described in the last chapter. If sporidia of a suitable 
species of Melampsora or Melampsoridium blow on to leaves 
of larch under suitable conditions for germination, infection 
is almost certain, however healthy or unhealthy the larch 
may be. The canker fungus, on the other hand, is largely 
dependent on finding trees which are not growing with full 
vigour. This fungus is always with us on the dead branches 
of healthy trees as much as on those of unhealthy trees. 
Whether or no it is to become parasitic depends on its 
opportunities for infection, and this is chiefly determined 
by the vigour of the trees. With the rust diseases, then, 
we are pathogenetist ; with the canker, predispositionist. 
With most other diseases we are somewhere betwixt and 
between. 
