62 DISPOSITION OF PLANTS TO DISEASE. 



to hail. Juicy fruits whose epidermis has become broken, soon 

 rot unless a protecting layer of wound-cork is rapidly formed. 

 Wounds in the wood present an entrance-gate to numerous 

 Polyporeae, otherwise unable to penetrate. In the case of 

 wounds to the wood of spruce or young branches of pine, a 

 protecting crust is frequently formed by the rapid excretion 

 of resin from the injured surface.^ 



The disposition of a host-plant depends then on some inherent 

 condition of the protoplasm or on some accidental circumstance. 

 The latter may be anatomical and due, for example, to thickness 

 or other property of the cuticle, or to a hair-covering ; it may 

 be morphological, from some defect, say on the part of the leaf 

 in not allowing easy escape of water. The disposition may be 

 periodic {e.g. in youth or at flowering), or it may be permanent. 

 It may be generic, or confined to some particular variety or 

 species, or it may be individual. It may be normal or abnormal. 



The practical lesson of this chapter has been that we should 

 cultivate our plants so as to avoid the conditions which dis- 

 pose them to disease, and that we should rear and cultivate 

 these kinds least liable to injury from disease. The considera- 

 tion of these points forms the subject of our next chapter. 



' Resin is in itself not antiseptic, and in the fluid condition inside plants 

 aflfords no barrier to fungus-hyphae of Peridermium plni and Nectrla cucarbituia ; 

 the hardened crust on a wounded surface serves, however, to keep ofif spores 

 from the plant tissues, and prevents the penetration of germ-tubes. 



