'217 



a diminished vitality, which render trees more liable to injury 

 by fungi and insects, for loss of increment and for interference 

 with reproduction. It has been noted above that different 

 species vary in their power of resisting excessive heat, and 

 while some plants are very sensitive to damage from fires others 

 are less so. The effect of the fire on any particular species of 

 plant depends mainly on the intensity of heat produced by the 

 fire and on the state of development of the plant itself. A % 

 fire which may be beneficial shortly after the fall of the seed, 

 by hastening germination, would be very destructive after ger- 

 mination has actually commenced. Seedlings of deciduous 

 species which have their serial parts destroyed by fire 

 in the resting season may be very little damaged, while 

 others burnt in the vegetative season may be seriously 

 injured. The seeds of some species also are readily destroyed 

 by fire, while those of others are protected from injury by hard 

 or corky coverings, etc., and in the case of some species the ger- 

 mination of the seed appears to be aided rather than hindered 

 by fire. 



196. Finally, it must never be Necessity of 



forgotten that a factor, in addition to any direct beneficial j^jjjjf the 

 or injurious action which it has on the development of Beneficial or 

 any particular plant, may also exercise a by-no-means less injurious 

 important indirect beneficial or injurious action, by Eff ? c t of 

 affecting the development of correlated organisms. Thus 68 

 winds may be directly beneficial in aiding fertilisation 

 and the distribution of seeds of a certain species, while they are 

 indirectly injurious by performing the same services for an 

 injurious plant competitor, or by distributing the spores of an 

 injurious parasitic fungus. Again fires may be indirectly 

 injurious by damaging symbionts, such as useful soil bacteria 

 or fungi, and indirectly beneficial by destroying, or retarding 

 the development of, injurious plant competitors or parasites. 



