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after June or July. In the following year, or in the second, at the latest in 

 the third year, after the appearance of the silver leaf, the branch dies. In 

 the specimens which I could examine after the lapse of a year, the 

 phenomenon appeared often on the other branches after the dead branch 

 had been removed, so that, for the present, I have formed the hypothesis 

 that the silver leaf is an absolutely certain precursor of the death of a branch. 

 It is found most wide-spread among apricots. I found the phenomenon 

 also in plums and apples. 



The change begins in the older leaves of the spring growth, the youngest 

 more often escape ; likewise the late shoots developing suddenly in old wood 

 from preventative eyes. First of all only a certain dullness of color is 

 found, a loss of the gloss in places and, as it seems to me, an increased 

 amount of air in the intercellular spaces between the various palisade cells 

 or between them and the epidermal cells. Gradually the dull places become 

 whitish, in fact because of a glandular breaking up of the epidermal cells 

 between the finest ramifications of the veins which remain green. This 

 loosening up consists of a dissolving, in places, of the connection between 

 epidermis and palisade parenchyma. 



AderholdS who also observed the disease in cherries and found that the 

 cells of the epidermis mutually separate from one another, could prove that 

 the variations from the healthy leaf, in places displaying the silver leaf, were 

 found in the solvability of the intercellular substances (middle lamellae). 

 He surmised that the intercellular substance in the diseased organs consisted 

 of more soluble pectin compounds than in the the healthy leaf and, since the 

 calcium compounds of pectic acid represent insoluble conditions, the theor}^ 

 is pertinent, that the disease may be due to a lack of calcium. 



According to this theory, the disease would also belong in the group of 

 phenomena, due to deficient moisture and nutritive substances ; only it must 

 be emphasized in this, that the content of moisture and nutritive substances 

 in the soil cannot come under consideration here, but that only in the plant 

 itself can it be manifested locally. And this circumstance points to dis- 

 turbances in the vascular system. This is favored also by the fact that the 

 branches with silver leaf die prematurely. 



The apricots and plums which I observed showed gummosis and the 

 apple trees suffered from the gnawing of bark beetles. It might be possible 

 to strengthen the whole organism by rejuvenescence of the diseased trees 

 and by supplying calcium. 



The Water Core of Apples. 



In the same way the phenomenon may be traced to the local vascular 

 disturbances in which individual fruits of a tree in part, or as a whole, re- 

 main hard and become glassy and transparent, — develop less color and are 

 tasteless. 



1 Aderhold, R. Notizen liber einijre im vorigen Sommer beobachtete Pflanzen- 

 krankheiten. Zeitschr. f. Pflanzenkrankh. 1S95, p. 86. 



