_Wood-nodules_ or _Sphaeroblasts_ are curious marble-like masses of wood which protrude with a covering of bark from old trunks of Beeches, etc., and can be readily dug out with a knife. The nodule has arisen by the slow growth of the cambium of a dormant bud, the base of which separated at an early date from the wood beneath; the cambium then closed in over the base and laid on thickening rings all round the axis of the bud except at the extreme apex. When the separation occurred the cambium of the wood beneath covered over the previous point of junction, and thus the woody bud was pushed out with the bark, and now protrudes covered with a thin layer of the latter. Similar nodules are occasionally found on Apple trees. NOTES TO CHAPTER XXIV. For further information on Cankers the student should read Marshall Ward, _Timber and some of its Diseases_, Chapter X. Further, the discussion as to the causes of canker in Frank, _Krankheiten der Pflanzen_, B. I., p. 207, and B. III., pp. 167 and 172, and various papers in _Zeitschrift für Pflanzen-krankheiten_. CHAPTER XXV. EXUDATIONS AND ROTTING. _Tumescence--Rankness--Bursting of fruits, etc.--Root rot--Rot of fruits--Bulb diseases--Flux--Honey-dew--Slime flux-- Resinosis--Gummosis--Manna._ I put together in one artificial class a varied group of diseases, the principal symptom of which is the escape of fluids from the tissues, under circumstances which betray an abnormal state of affairs, often obvious, but sometimes only to be inferred. In many of these cases bacteria abound in the putrefying mass, and some evidence exists for connecting these microbes causally with the disease in a few of the more thoroughly investigated cases, but in no case has this been sufficiently demonstrated; and considering the ease with which bacteria gain access _via_ wounds caused by insects and fungi, as well as by other agents, the necessity for rigid proof must be insisted upon before we can accept such alleged examples of _Bacteriosis_.