HEALTH AND DISEASE, 97 



though they are apt to be abnormally thin and 

 may be small. Little or no reserves are stored 

 anywhere, and the watery tissues contain danger- 

 ously diffusible substances which may render 

 them an easy prey to parasitic fungi. Here 

 again, however, if the disturbance of equilib- 

 rium has not gone too far, and if the season 

 permits, the new leaves may come into full 

 activity and the situation be saved by transpiration 

 and assimilation gradually increasing and restoring 

 the equilibrium. But, as before, the plant has 

 suffered, and shows the effect in its weak shoots, 

 retarded flowering, and other ways. 



Such plight as is here described may actually 

 be attained in greenhouses where over-watering is 

 the fault, and even in the open it is not uncommon 

 in rainy summers, or in plantations where dominant 

 trees get the upper hand and partially shade more 

 slowly growing species, or in fields where rank 

 grass is allowed to overwhelm crops of lower 

 stature. 



Now it will be evident that either of these 

 typical cases of temporary disturbance of functional 

 equilibrium may be carried too far : in the first 

 case the plant may wilt and wither, in the second 

 it may rupture and rot, to take these eventualities 

 only. And yet it is difficult to call these indis- 

 positions diseases : they are rather examples of 

 extreme departures from the normal standard of 

 health, just on the borderland between health and 

 disease. A step further, as it were, and disease 

 supervenes : certain tissues die from want of water, 



G 



