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pointed out that ‘‘the leaves which fade after their supporting 
ranch has been killed by heat, fade in a different manner from 
those which wilt owing to a lack of water. In the former case 
the margin of the leaf first becomes darkened and this darkened 
region gradually invaded the leaf between the veins. It then 
dries and shrivels whilst the green parts immediately round the 
veins remain comparatively fresh. As this change is taking place 
these veins usually become pink and finally brown. This colora- 
tion is particularly noticeable when the leaves are viewed with 
transmitted light. Shrivelling and withering of the leaf, except 
at the edges, does not occur until after these changes are com- 
ete’’. ‘* On the other hand, when leaves fade simply from an 
plete 
tw 
poisoning by the products of morbid and degenerative changes, 
and the effects merely of a shortage of water. 
Now it has already been noted that in the present specimen 
of Aesculus Pavia the leaves at first were limp and flaccid but 
brittle, and during the subsequent week the leaves merely 
withered in the manner characteristic of drought, and without 
any of the symptoms of poisoning. 
The desiccated condition of the tissues of the stem, and the 
ich the leaves faded, were strong presumptive 
To determine the soundness of this hypothesis, a careful ex- 
amination, using microchemical methods, was made of the tissues 
immediately above the diseased zone and these were compare 
minutely with corresponding tissues from other parts of the stem. 
No trace could be detected of any deposition of morbid products 
either in the walls or in the lumina of the tissues in question, and 
although, as will be noted later, tyloses were not infrequently 
present they were not more abundant in this region than in any 
other portion of the tree. Thus although at first it had appeared 
probable that the death of the Aesculus Pavia under considera- 
tion was either a direct result of the suppression of the vital 
activities of the cells of the medullary rays and wood-parenchyma 
