844 JOURNAL OF THE E< )YAL HORTICULTURAL SOCIETY. 
of the tissues and produce a special fermentation which gives off a greasy 
smell as of butyric acid. 
As comparatively few trees are attacked by this sap exudation vre need 
hardly trouble to consider them in our investigation. 
In the same way we can omit the few trees many of whose leaves are 
sprinkled with black spots and covered on the under side with a kind of 
efflorescence. It is practically certain that these are produced by the 
parasitic fungus Taplirinanlime, whose attacks are not dangerous. Neither 
the dampness nor the dryness of the soil could be the cause of the change 
in the wood we are investigating, because in the plantations on the banks 
of the river Mansares, where the soil is wet, as well as in dry places, the 
trees are affected in the same manner ; and as the subsoil in all the 
Elm groves is generally accessible to deep roots, it does not seem hkely 
that the trees could become root-bound and thus set up disease in the 
wood. 
To my mind we have to deal with the wood disease known to woodmen 
under the names of '"'wood frost,"' "curling frost"" and shocked " or 
thunderstruck wood.'" 
I think the disease is produced by malnutrition. One cannot attribute 
it to any parasite. It is simply a physiological disease or disintegration. 
^Vith a defective nutrition the tissues are badly constructed, there are 
no strong walls between the fibres and cells, and consequently the wood 
is feeble, soft, and of small durabihty or cohesion. 
In such a condition a low temperature contracts the tissues, and at 
the same time the sap contained in them expands. These two antago- 
nistic forces strain the cells and ducts, and, the structure of both these 
organic bodies being frail, their walls are unable to resist the combined 
pressure and give way. The exterior tissues, which are the weakest and 
least formed, are most intluenced by cold, and break first. In consequence 
of these breakages the wood itself is exposed, and the split opens wider 
and wider until at last it reaches the very heart of the trunk. The trunk 
is not generally transformed into perfect wood. The timber consequently 
remains soft, light of colour, and loose-grained — in one word, useless 
wood. 
By regulating the nutrition of the tree, one can arrange that the 
elements of the tissues shall be better constituted, more sohdly formed, 
and iQ themselves more adherent and consequently possessing more regular 
tissue, harder, and ofiering greater resistance to the action of low 
temperatures. 
The Elms I am speaking of grow on lanes that are full of humus, but 
not particularly rich in phosphoric acid. The withered leaves that fall 
from the trees and the great quantity of moss form a kind of manure. 
There is undoubtedly plenty of nitrogen m the soil. and. considering the 
natural humidity, it is easy to understand that the tree- grow very rapidly. 
AVith watery and nitrogenised sap the anatomical elements of the bark 
contain little consistency, wanting mineral salts to harden the tissues 
and repress the over-luxuriant growth often found where nitrogen is 
superabundant and there is too much moisture. 
The way to prevent this is to clear the ground of the moss, and from 
time to time take away the fallen leaves and add phosphoric acid and 
