136 Butler. — A Study on Gummosis of Primus and Citrus , with 
about recondensation. Such phenomena of solution and recondensation 
are perfectly well known in the plant kingdom, but I think that to ascribe 
gummosis to such an analogous process is hardly warrantable. It seems to 
me, therefore, that gummous degeneration is to be explained in some other 
way than by assuming the pathological action or excretion of an enzyme 
acting in the presence of the factors growth and water. But how shall we 
explain it ? I am inclined to believe that were the genesis and development 
of the cell-wall better known gummosis could be explained on a purely 
physico-chemical basis, but to venture to do so in the present state of our 
knowledge would have but a single issue : failure. 
8. Preventive and Remedial Measures. 
It will be well, before discussing the preventive and remedial measures 
employed against gummosis, to recapitulate briefly the conditions under 
which the malady develops. 
Gummosis affects trees planted in moist retentive soils and poorly 
drained soils ; excessive irrigation is inducive in any soil, but particularly 
so in those that, either from their situation, the nature of their subsoil, 
or their physical composition, are classed as moist soils. Trees planted in 
rich soils, or highly fertilized, especially with nitrogenous manures, are 
more subject to the disease, ceteris paribus , than those grown in poorer soils 
and in orchards less intensively cultivated. Plantations in which intercalary 
cultures requiring a large amount of water and high fertilization, i. e. vege- 
tables, are grown soon become decimated. Various parasitic Fungi, boring 
and gnawing insects, wounds due to pruning, hailstones, sun-scald, accidental 
abrasions during cultural operations due to ploughing, cultivating, or fruit- 
gathering, inordinate pruning during vegetative activity, unequal growth 
between stock and scion, planting the trees in such a manner that the 
union between stock and scion occurs below ground — to all these various 
agencies gummosis has been justly ascribed. In the following remarks on pre- 
ventive and remedial measures, however, some of these causes of gummosis 
will not be further considered. When the cause of the disease is traceable 
to Fungi or insects, sun-scald, or abrasions incidental to cultural operations, 
the remedies are obvious, and therefore need no particular consideration. 
Preventive measures. As gummosis does not occur unless the affected 
trees are growing rapidly and their tissues are, at the same time, sapid, 
there will be four possible methods, and they have all been employed, of 
preventing the development of the disease. 
1. Drainage, and, when irrigation is practised, more rational distri- 
bution of the water. In draining an orchard, or land intended for an 
orchard, care should be taken to make the drainage efficient ; but whether 
this shall be accomplished by tile draining, open ditches, by growing the 
trees on ridges, or by combining two or more of these methods, is a question 
