Gall (botany)

“ The Gall-flies, Cynipidæ, are the easiest of the families to collect, because of their abundance and because of the ease with which they may be reared. Their galls occur in enormous variety on oaks of various species and also upon brambles and certain common weeds. These should be collected when mature and be kept in glass jars. The Gall-flies and inquilinous and parasitic species may thus be easily obtained, the former appearing at particular seasons and the latter emerging from the galls at all seasons of the year, and sometimes continuing to escape for a period exceeding two years. ”

“ Still more singular is the gall found in the catkins of the oak. The flies deposit their eggs in the stalk of the stamen-bearing flowers, which in consequence become adorned with what appear to be straggling bunches of currants or bird-cherries. Placed at short distances from each other on the thread-like stem, these excrescences so much resemble 151currants in size, shape, and mode of growth, that they have been named “currant galls.” ”

“ The dipterous gall-formers include the gall-midges, or gall-gnats (Cecidomyidae) , minute slender-bodied insects, with bodies usually covered with long hairs, and the wings folded over the back. Some of them build cocoons within their galls, others descend to the ground or become pupae. The true willow-galls are the work either of these or of saw-flies. Their galls are to be met with on a great variety of plants of widely distinct genera, e.g. ”

“ These bright colours can be of no service either to the gall-forming insect or to the tree, and probably are the direct result of the action of the light, in the same manner as the apples of Nova Scotia or Canada are brighter coloured than English apples. The strongest upholder of the doctrine that organic beings are created beautiful to please mankind would not, I presume, extend this view to galls. According to Osten Sacken's latest revision, no less than fifty-eight kinds of galls are produced on the several species of oak, by Cynips with its sub-genera ”

“ The same gall-insect may induce totally different galls on different plants, or even on different parts of the same plant, and different insects call forth different galls on any one plant. These facts point clearly to the co-operation of both plant and insect in the gall-formation, and the best hypothesis yet to hand is to the effect that a gall is a hypertrophy of cells, the normal nutrition, growth, and division of which have been disturbed owing to the action of some poison or other irritant derived from the insect, or fungus, or other organism. ”

“ Artichoke Gall of the Oak-bud, with Gall-fly (Cynips quercus gemmæ) , natural size, and its ovipositor (a) magnified.
From the very nature of the process of forming willow-galls, bedeguar, and the artichoke of the oak, whatever [406] theory be adopted, it will be obvious that their growth must be rapid; for the thickening of the exuded sap, which is quickly effected by evaporation, will soon obstruct and finally close the orifice of the puncture made by the parent insect. It is accordingly asserted by Réaumur and other observers, that all the species of galls soon reach their full growth. ”

“ Only experience with each species, involving continued observation of specimens of the galls, and obtaining of such information as may be supplied by the size of the gall, the degree of development shown by the insect within the gall, etc., can supply information of the approach of the emergence date for a particular species. Most of the solid, hard, woody, or dry-shelled galls may be kept successfully for many months, but the adults of soft, spongy, or hollow, succulent galls cannot be raised if the galls are gathered more than a week or even a few days before the insects are due to emerge. ”

“ Often the gall bears no visible resemblance to the structures out of which it is developed; commonly, however, outside the larval chamber, or gall proper, and giving to the gall its distinctive form, are to be detected certain more or less modified special organs of the plant. The gall of Cecidomyia strobilina, formed from willow-buds, is mainly a rosette of leaves the stalks of which have had their growth arrested. ”

“ It is common enough in this locality, and I have met with more than a dozen specimens of it. It is always found on the same plant (apparently a species of Ficus) , and I have only seen one specimen of the plant not infested by the gall-fly. The part attacked seems to be always the base of the leaf, or possibly an unopened leaf-bud. The gall-capsules at first are pale yellowish green, with irregular reddish staining. As they mature they become dark green, and are aggregated together into a dense mass, through which the leaves continue to grow, but in a stunted and irregular manner ”

“ But there is a mouth on this silly sort of head, and the grub eats. What it eats is part of its own house!
The houses, or galls, as the entomologists call them, are of course not actually made [Pg 291] by the insects that live in them; they are made by the oak-tree on which they are. But they are only made at the demand, so to speak, of the insects. That is, the oak-galls are formed only where a gall-insect has pricked a live leaf or stem or twig with her sharp, sting-like little egg-layer, and has left an egg in the plant-tissue. Nor does the gall begin to form even yet. ”

“ The adults were cut from the type gall collected by Couper about forty years ago. The gall of this species was mentioned by Jarvis but the adults have not been described previously. The gall is a very simple and primitive sort of plant deformation, being more primitive than in most of the species of Diastrophus. D. fusiformans and D. fragariæ approach it in this respect. The adults are typical of the species of the genus and are readily separated by the key characters given in the description. ”

“ I believe that this is as impossible as that the leaf of an oak should produce a gall, without having been pierced by a gall-producing insect, as a result of the thousands of antecedent generations of oaks which have been pierced by such insects, and have thus ‘acquired’ the power of producing galls. ”

“ The gall has a gummy tendency, and will glue together the fibers of the feathers, and, besides, it has a great attraction for moisture, and, in humid weather, will become damp, and therefore produce mould; the other alkaline substances must also be used with much caution and quickness, because they have the power of changing the colors of the plumage, so that they are most useful in white plumage, and therefore should only be used on colored feathers, where gall cannot be procured. ”

“ Now the gall-insects come, as has been said, out fig, and they are engendered from the seeds. The proof given of this is that, when they come out, there are no seeds left in the fruit; and most of them in coming out leave a leg or a wing behind. There is another kind of gall-insect which is called kentrines; these insects are sluggish, like drones, they kill those of the other kind who are entering the figs, and they themselves die in the fruit. The black kind of wild fig which grows in rocky places is most commended for caprification, as these figs contain numerous seeds. ”

“ As why it is that two galls made by two different kinds of gall-insects, but in the same parts, as leaves, of the same oak-tree, should be so different, or why the galls in different kinds of trees, though made by the same kind of insect, should be alike, as they usually are. And why with some kinds of the house-dwellers the children grow up to be different from the mother, but their own children grow up like the grandmother, and different from themselves. ”

“ Cotypes.—Cotype females, males, and galls in The American Museum of Natural History, the Academy of Natural Sciences of Philadelphia, and the Museum of Comparative Zoology.
This gall is the better-known form of the species, due apparently to its longer persistence on the tree. The gall very closely resembles that of Neuroterus batatus batatus, from specimens of which it is often difficult to distinguish this species. The more highly distinct larval cells of noxiosus is often a good basis for making the distinction. ”

“ Within the galls, the naked, helpless worms are at once protected from exterior assaults of every kind and provided with an unfailing supply of food which they can reach without effort, so that their development goes on without obstruction of any kind. According to A. Schenck, the gall-nuts of the rose are adapted to the shelter and support of the larvæ of more than two hundred species of flies, and those of the oak are also the home of numerous varieties. ”

“ The leaf-infesting stages of the insect cause pocket-like galls to form, which open on the upper surface of the leaf by a narrow aperture concealed under a tuft of delicate hairs (Fig. 9, 5) . In each gall the aphid matures and deposits several hundreds of eggs, from which wingless females hatch; these wander to other leaves, and each insect forms a new gall for itself. Several generations develop thus, but later many of the offspring migrate underground and join the root-infesting colonies. ”

“ On the roots, the young lice attach themselves singly or in little groups, and thus hibernate. The male gall-louse has never been seen, and there is every reason to believe that he has no existence. Nor does the female ever acquire wings. Indeed, I cannot lay too much stress on the fact that gallæcola occurs only as an agamic and apterous female form. It is but a transient summer state, not at all essential to the perpetuation of the species. ”

“ From this time the gall-nut no longer derives from the tree those juices which were necessary for the nourishment of the insect, but dries up, and loses the greater part of those qualities which make it valuable in commerce. The Aga of the district takes care that the cultivators traverse frequently, at the time of the harvest, the hills and mountains which are covered with this oak. He has an interest in obtaining galls of good quality, because he levies a tax on the produce. ”

“ Most of the members of each community are active and roving in their dispositions, and show no tendency to undue distension of the nether extremities. They go out at night and collect nectar or honey-dew from the gall-insects on oak-trees; for the gall-insect, like love in the old Latin saw, is fruitful both in sweets and bitters, melle et felle. This nectar they then carry home, and give it to the rotunds or honey-bearers, who swallow it and store it in their round abdomen until they can hold no more, having stretched their skins literally to the very point of bursting. ”

“ H. cordiformis seems to bear much fewer species than H. ovata or H. alba. In the present list, the report of the gall upon a particular species of tree does not at all imply that it does not occur on others.
Having had the opportunity to give attention to gall collecting in three rather widely separate localities, eastern Connecticut, southern and northern Ohio and eastern Kansas, some observations on the geographical distributions of the hickory itonids are here briefly presented. [Pg 40]
It is sometimes stated that the distribution of gall insects is similar to that of their host plants. ”

“ It begins only after the young gall-insect is hatched from the egg, or at least begins to develop inside the egg. Then the gall grows rapidly. The tree sends an extra supply of sap to this spot, and the plant-cells multiply, and the house begins to form around the little white grub. Now this house or gall not only encloses and protects the insect, but it provides it with food in the form of plant-sap and a special mass or layer of soft, nutritious plant-tissue lying right around the grub. So the gall-insect not only lives in the house, but eats it!—Vernon L. Kellogg, “Insect Stories.” ”

“ The irritation thus produced causes a gall to form on the lower side of the leaf. In fifteen days the louse becomes a full-grown wingless female and proceeds to fill the gall with eggs after which it dies. In about a week females hatch from the eggs and migrate to form new colonies. Several generations of females occur in a summer. At the approach of winter the lice go into the ground where they remain dormant until spring when they attack the roots forming galls analogous to those on the leaves and passing through a series of generations similar to those above ground. ”

“ The grub still feeds, and the swelling becomes larger, until finally, when the insect ceases to eat, it is housed in the peculiar ball which we know as an oak gall. Each species of gall-maker is known by its house. ”

“ Small berry-shaped galls of the oak leaf, produced by Cynips quercus folii?
One of the most simple and very common instances of the nests constructed by gall-insects, may be found in abundance during the summer, on the leaves of the rose-tree, the oak, the poplar, the willow (Salix viminalis) , and many other [399] trees, in the globular form of a berry, about the size of a currant, and usually of a green colour, tinged with red, like a ripe Alban or Baltimore apple. ”

“ Of how the houses begin to form under the bark or leaf surface as mere little swellings and then break through and get larger and larger and take on their characteristic form and color. Of how we have to study the gall-dwellers with a microscope, [Pg 297] for the largest that we have found yet—the ones that make the big galls shown in Sekko's picture—are only one-fifth of an inch long, while others are not more than one-twenty-fifth of an inch long. Of how some kinds have to lay their eggs always on the same kind of oak-tree, while others prick different kinds of oaks. ”