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The struggle between the mycelium on the one hand, which tries to extend all round in the cortex, and the tree itself, on the other, as it tries to repair the mischief, will end in the triumph of the fungus as soon as its ravages extend so far as to cut off the water supply to the parts above: this will occur as soon as the mycelium extends all round the cortex, or even sooner if the effusion of turpentine hastens the blocking up of the channels.
The filaments of mycelium, under the same magnitude, appear exceedingly thin and finer than a hair. The shape of the conidia, though presenting some varieties, is, notwithstanding, always perfectly characteristic. Sometimes they resemble in appearance the segments of a semicircle more or less great, sometimes the wings of butterflies, double or single.
That it is a vital phenomenon, and due to the mycelium of a fungus, I do not in the least doubt, for I have observed it occasionally circumscribed by those black lines which are often seen to bound mycelia on dead wood, and to precede a more rapid decay. I have often tried, but always in vain, to coax these mycelia into developing some fungus, by placing them in damp rooms, etc.
If an affected stem is put in a moist chamber made from a covered or inverted dish, there will develop an exceedingly vigorous growth of snow-white fungous mycelium which, after a few days, bears numerous round shot-like bodies, at first light-colored, then becoming smaller and dark-brown. These are the sclerotia or resting bodies of the fungus.
Between these larger orange yellow vesicles the lens shows certain smaller brownish or almost black specks. Each of the vesicular swellings is a form of fungus fructification known as an Æcidium, and each of the smaller specks is a fungus structure called a Spermogonium, and both of these bodies are developed from a mycelium in the tissues of the leaf.
These groups of yellow spores burst forth in irregular powdery patches, scattered over the under sides of the leaves in July and August: toward the end of the summer a slightly different form of spore, but similarly arranged, springs from the same mycelium on the same patches.
In 1860-65 I saw the grape in a piteous plight: the huge bunches were composed of dwarfed and wilted berries, furred and cobwebbed with the foul mycelium. The produce fell to 100-150 pipes, and at present only some 200 to 300 are exported. The Peninsula and the West African coast take the bulk; England and Germany ranking next, and lastly Spain, which used the import largely in making-up wines.
The annual rings are formed as usual on the opposite side of the stem, where the cambium is still intact, or they are even thicker than usual, because the cambium there diverts to itself more than the usual share of food substances; where the mycelium exists, however, the cambium is destroyed, and no thickening layer is formed.
When they are perfectly developed, they are distinctly separated from their filament of mycelium by a septum that is to say, by limiting lines plainly marked. It is not rare, however, to see the individual sporangia perfectly isolated and disembarrassed of their filament of mycelium floating in the water.
It is also stated that only young pines are badly attacked by this form: it is rare to find Æcidia on trees more than twenty years or so old. The epidermis is already ruptured at p by the pressure of the young Æcidium. Much more disastrous results can be traced directly to the action of the mycelium in the cortex.
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