Under ordinary circumstances atrophy is exemplified by the presence of rudimentary or imperfect organs, as, for instance, in Pentstemon, Scrophularia, &c., where one stamen is atrophied.
For convenience sake atrophy may be divided into abortion and degeneration, the first including cases where, from arrest of development occurring at an early stage, organs are present; but in a much smaller and more rudimentary condition than usual, their form and general appearance, except so far as regards their dimensions, not being materially altered. On the other hand, in cases of degeneration, development is not entirely checked, but rather perverted, so that not only the dimensions are lessened, but the form is altered.
CHAPTER I.
ABORTION.
The sense in which this term is here understood has been explained in the preceding paragraph. It is only necessary to say further, that cases of abortion are to be distinguished from those of suppression, on the one hand, and those of degeneration on the other. In suppression there is from the first an absolute deficiency of a particular organ. In degeneration the part is present, but in a diminished and perverted condition. In abortion it exists, but in a stunted and dwarfed, but not otherwise permuted state.
Abortion of axile organs.—When the main stem is arrested in its growth, the habit and general appearance of the plant are materially altered, as in the so-called stemless plants, plantæ acaules. In these the internodes are so slightly developed that the leaves are closely crowded in tufts or rosettes. When this shortening of the stem (acaulosia) occurs, without other considerable change in other organs, the deviation is classed under the head of variation rather than of monstrosity; and, indeed, in very many plants, this arrested growth of the axis is the rule rather than the exception. When occurring in an abnormal manner, atrophy of the stem is most frequently attended by other more or less grave alterations in other structures; thus Moquin-Tandon[522] cites an instance of Camphorosma monspeliaca, wherein the stems presented the form of very short, hard, woody tubercles, thickly clothed with deformed leaves, and invested by a vast number of hairs, longer and more dense than usual. A similar deformity sometimes occurs in an Indian species of Artabotrys; in these specimens the branchlets are contracted in length, and bear numerous closely packed scaly leaves, densely hairy, and much smaller than ordinary.
Spines and thorns may he looked on as atrophied branches, and seem to result from poorness of soil, as the same plants, which, in hungry land, produce spines, develop their branches to the full extent when grown under more favorable conditions.[523]
In the birch an arrest of development in some of the branches is of common occurrence. The branch suddenly ceases to grow in length; at the same time it thickens at the end into a large bulbous knob, from which are developed a profusion of small twigs, whose direction is sometimes exactly the reverse of that of the main branch. ([See p. 347.])
The branches of the common spruce fir, especially the lateral ones, when attacked by a particular species of aphis, are very apt to be developed into a cone-like excrescence.[524]
A shortened condition of the flower-stalks occurs occasionally, greatly altering the general character of the inflorescence. This has been observed in pelargoniums and in the Chinese primrose, in both of which the effect was to replace the umbellate form of inflorescence by a capitate one.