BLIGHT. 129 



from such conditions, and all surface-rooted ones from long- 

 rooted trees are necessarily compelled to rest, especially if 

 carrying a heavy crop, then, stimulated by the plowing, fertil- 

 izing and winter pruning described, if a mild spell occurs any 

 time in winter, a movement of the sap is sure to take place. 

 It may not show itself in leaves or blooms, for it does not in 

 the grape; but the movement will be there, and if that motion 

 be checked by a freeze, and the sap stagnate or sour, so to> 

 speak, for a month or more before growth starts again, then 1 

 blight is certain to occur. We have furnished, then, the con- 

 ditions for an abnormal development and propagation by mil- 

 lions of the bacteria, and I pointed out above the course of 

 that development. The blooms first show it, next the fruit 

 spurs, then after warm rains and muggy weather later on, the 

 tender shoots blacken and droop, and the disease spreads to 

 the limbs around the base of the fruit spurs. Now, then, for 

 some of the unexplained phenomena of blight. 



1. Why do the most vigorous trees in well cultivated 

 ground surfer oftener than the weakly ones alongside, or in 

 grass? Because, given the conditions for blight described,, 

 the vigorous tree will certainly be most susceptible to the 

 stimulating treatment named, and in addition, the owner is- 

 sure, in his desire to produce a more uniform appearance of 

 the orchard, to cut back the long canes on it very severely,, 

 while the weakly tree often, in fact generally, escapes the 

 knife altogether. I years ago treated trees just that way 

 myself, and know that the sap in a heavily pruned, vigorous 

 young tree will be in full flow or motion in a warm spell in- 

 winter, when the other is still quite dormant, and fails to fur- 

 nish the conditions for the bacterial development within. 

 The germs were in the sap of the weaker one also, but, the 

 proper conditions not being furnished, failed to develop, just 

 as in every cholera or yellow fever epidemic, certain persons- 

 escape those diseases, and yet in food, water and air the germs 

 must have gotten into their blood, if not there before. 

 Science has yet to determine the exact conditions in man and 

 trees that govern their development. 



2. Why has blight never appeared in California? First, 



9 HORT. 



