38 



W. A. CANNON 



pears with the complete and sudden removal of the chaparral. 

 This is shown by the disappearance of much of what herbaceous 

 growth is characteristic of this formation with its destruction, 

 and, as we have seen, by the death of the pines, under conditions 

 to be given directly. 



The roots of the Monterey pines, so far as has been observed, 

 are in part very shallowly placed. Long and large roots of 

 mature plants lie close to the surface of the ground and are often 

 in part uncovered by the rains. In old trees these roots serve 

 in part for mechanical support, but the absorbing roots are also 

 in part superficially placed. The laterals of the young pines 

 extend outwards from the main axis for a comparatively longdis- 

 tance and lie mainly within 6 inches of the surface. The roots 

 are so well developed that the transplanting of trees grown in 

 nature is difficult except in the very young specimens. From 

 observations made on the roots of the species, therefore, it ap- 

 pears that changes in the water relations of the upper soil layers 

 may be of importance in the survival of the individual. This 

 conclusion is of especial significance when the long summers' rain- 

 less character of the climate is taken into account. 



The leading events which bring about the death of mature 

 pines, therefore, under conditions given above, may be briefly 

 given. The chaparral affords a protection to the soil against 

 excessive drying out in summer. The root-systems of pines 

 which invade the chaparral adapt themselves in position to this, 

 and when the chaparral is removed, the more arid soil in which 

 the roots find themselves does not yield adequate water supply. 

 Starvation is the ultimate result. Support is given this hypoth- 

 esis in the springing up and thriving of the younger pine genera- 

 ation, after the cutting of the chaparral. 



