266 REPORT OF THE HORTICULTURAL DEPARTMENT OF THE 
apples, as in the case of members of the genus Prunus, probably 
does not take place and in the few cases where the “ shot-holes ” 
in apple foliage are to be found in bordeaux injury, the lifeless 
tissue has been blown out or removed by some other mechanical — 
means as by rain or a later spraying. 
The injury is greatest on young leaves and develops more 
quickly on young than on mature leaves. Thus, leaves at the 
end of shoots almost always show more injury than those at the 
base of shoots. It is reasonable to assume that this is because 
the young leaves are not so well protected by thickened cell 
walls as the older ones. 7 
There were always to be found among the defoliation from 
injury some yellow leaves which did not show the dead, brown 
spots. I am wholly unable to say whether these turned yellow 
and dropped from bordeaux injury or otherwise. I could not, 
it should be said, establish a definite proof that there was’ copper 
in either the dead brown spots of leaves showing these spots 
or in the yellow leaves, though the tests with iodide of potassium 
may have lacked proper management. 
From examination made I can form no conclusion as to how 
the dissolved copper salt enters the ‘cells of the leaves. 
Schander® found on leaves of Phaseolus vulgaris that the 1in- 
jury always started from the base cells of the plant hairs. 
Bain® found with apple, grape and peach leaves that the injury 
is greatest along the veins because “the cuticle is more per- 
meable there;’ and according to the same author “it occurs 
at definite points under and around spots of copper hydrate 
because the cuticle happens to be more permeable at these 
points.” All of my observations seemed to point to but one con- 
clusion; namely, that the dissolved copper salts pass osmotically 
into the cells of the leaf surface, and of the upper surface ~ 
chiefly, though occasionally of the lower surface. This seems 
to me to be the case because the brown spots are nearly always 
under the bordeaux stains. Muth®™ reached practically the same 
conclusion in his work with'the grape. I could see nothing to 
lead me to think that the copper solution entered through 
breathing pores or leaf hairs, as in the fruits, though I must con- 
fess that the examinations of leaves were not satisfactory. The 
——— 
* Schander (53, p. 580). 
* Bain (4, p. 98). 
° Muth (46, p. 7). 

