The purple pitchers of the first phase are provisional stations in which the Lice prepare for wholesale colonization. Each of these humble cottages has its Plant-louse from the foot of the tree. The solitary, who was herself hatched from a germ, makes haste to give birth to live youngsters, who gradually spread over the new leaves, and die. Then the true galls come, the great cities which will provide room for several generations. Here again, all the five classes of specialists between whom we have discriminated set to work, all labouring independently at the first filling out of the cabins. Mutual assistance will come later. May arrives; and already the simpler galls begin to grow: the lateral folds which, bent back upon the edge, become so many green hems. Beneath the awl of the black Louse, patiently pricking away at the leaf, a narrow border curves inwards from the edge. The line of attack measures a couple of centimetres. [65] When it has worked long enough at this or that point, the tiny insect changes its place and goes elsewhere to begin all over again, standing motionless while its implement performs its functions. Now what is the atom doing thus to warp what would be flat under natural conditions? Merely implanting its sucker. The prick of a needle, however skilfully guided, would bruise the tissues without affecting their form. The little insect must therefore instil a certain virus, which provokes an exaggerated flow of sap; it injects an irritant poison and the plant reacts by the swelling of the wounded parts. And now the hem is growing wider, with a slowness that defies our scouting: as well try to follow with the eyes the growth of a blade of grass. It is now a slanting roof, a gaping fold. The Louse is in the angle, at her post, doing her duty as a turncock. With her fine probe she stimulates and controls the flow of sap. In twenty-four hours the roof completes its descent, pressing tightly against the leaf. It is a lowered trap-door; but the mechanism of the structure works with such caution that the tiny insect, far from being crushed between the two thicknesses of leaf, retains its liberty of movement and moves about inside the fold as it would do in the open air. A curious instrument, the awl of the little black Louse! With our modern machinery a child’s finger, applied to this or that lever, this or that valve, sets enormous masses in motion. Similarly, the Louse, with her delicate probe, sets powerful hydraulic machinery going and trims the sails of a leaflet. She is, after her fashion, an engineer on a gigantic scale. The spindle- or ear-shaped galls make their first appearance on the edge of the leaves in the form of narrow crimson borders. Soon the walls grow thicker and become gnarled and fleshy, expanding into excrescences from which all green is excluded.