Plant Galls.

Oamaru Mail, Volume XXXI, Issue 8835, 15 July 1905, Page 4 (Supplement)

Plant Galls.

The habit that some insects have of depositing their eggs in the stems or the leaves of plants, where the wormlike larva} hatch and live until they are ready to metamorphose into the winged form of adult life, reacts on the plant to produce the peculiar deformations of structure called galls, that are of so much interest, both from the standpoint of factors influencing the mode of growth of a plant and from the remarkable nature of the galls taeniae! ves, one kind of gall, growing on the oak having come into especial prominence on account of its use in the manufacture of invisible ink, the same gall, mixed with certain chemicals, makes a very permanent kind of ink which in some States is required by law for certan records.

The subject is discussed by Dr M. 0. Howard in the last number of Annales des Sciences Jfaturelles (Paris). Some galls, as he shows, are produced by internal, others by external, parasites; they may appear at the end of the stem, or farther back, between the nodes of the stem, and in some instances they are found even on the roots

of the plant. The same kind of insect always produces the same kind of gall on the same kind of plant. One insect attacks the petiole of the poplar leaf and produces a hollow, spherical gall about half an inch in diameter, provided with a narrow slit on one side through which the insects maycome and go, and a myriad of them use this as a winter residence.

Another gall, on Bermuda grass, resembles a long braid of hair. The parasite in this case takes up its abode in the axis of the stalk of and by its presence interferes with the growth of the shoot, eo that the spaces between the leaves are much shortened and the leaves themselvs cannot attain full development, becoming more like scales. These stunted leaves, folded around the stem, give the characteristic braided appearance. In Slay, the larva of a certain fly hatches out in the stem of thyme, near the tip of the leaf-stalk, with the result that the stem never lengthens to any extent, the leaves grow very little and lose their color, and the general appearanc becomes that of a small cone.

Another kind of fly spends its larval life in the tip of the ground hemlock stem, affecting its growth in such a way that a loos© cone is formed of the half-grown, curved leaves.

Another gall-fly pierces the stem of young growing wheat to deposit its egg*, and when the larvse hatch, a small gall is formed that stunts the growth of the wheat and causes great loss to the wheat growers. All life is mysterious. What the formative, controlling principles of the simplest organism are, nobody knows. Whether the dynamics of life depend upon something related to chemical affinity, or to molecular arrangement, or to some entirely different condition, cannot be answered. Each individual begins life as a minute, protomorphie mass of living matter which in some way synthet-izes non-living material into substance Ike itself, and throughout existence compels it to take a certain form that is constant, in the main, for a given- species, although subject to some slight variations, perhaps, as tie result of living tinder more or less favorable conditions. But in the case of the formation of a gall, an external influence comes in with the egg and larva of the insect, and so affects the vital processes that the plant grows in a way entirely foreign to iteelf—a hollow sphere grows where a smooth stem should be, or a knotted woody structure with no resemblance whatever to the leaf that should have developed, normally. What is the nature of the new principle that produces such an effect. The controlling principle already in force becomes so modified under the action of the new principle that something entirely different results, capable of moulding a new type of structure, but as to the real nature of this, very little can be 6aid. Whatever it is, it affects the growth of the tissues in every particular, changing the form of the constituent cells, and the nature of their se-1 Tetions. I