HARDENING AND ADAPTATION 
The problems that arose in this line of work 
were among the most difficult he had ever 
encountered. Very much had to be taken into 
account,—the past of the tree, not only imme- 
diate but remote, its failures and successes 
under different environment influences, its 
limitations, its need of new blood by crossing 
or the restoration of its depleted veins through 
selection. For Mr. Burbank had come to look 
upon all plant life as being very closely allied 
to the life of man, open to many similar 
attacks, subject to many diseases, needing the 
keen eye of the physician and the dietarian, 
responding to heat and cold, light and shadow, 
inactivity and exercise. He early recognized, 
too, the importance of transference, the intro- 
duction of a fruit from a distant quarter of the 
globe, engrafting its life upon the life which 
was not coming up to its opportunities. He 
recognized that that which holds true in the 
human race,—that admixture of blood is desir- 
able, indeed is imperative at intervals, in order 
to prevent such physical decadence as follows 
the intermarrying of royal families,—held 
true sometimes in the vegetable world; there 
were certain families that needed new blood 
193 
