362 NATURAL SCIENCE. Nov.. 



efforts of nature proving powerless to remedy the pathological turge- 

 scence — a veritable atrophy ensues, the stamens wither and the resiant 

 gall languishes and dies." 



The mode by which, in the case of the oak-apple, the essential 

 changes are carried into effect and the development of the gall com- 

 pleted, is worthy our attentive study. I have already mentioned that, 

 in ovipositing, the parent cynips so disposes of her eggs that, for the 

 most part, they lie with their broad ends downwards towards the fixed 

 surface of the cut axis. As spring advances, this surface becomes 

 moistened by the rising sap ; and, influenced by the process, the first 

 range of pendent eggs is brought into direct and immediate relations 

 with it. 



About this time the embryo-larva hatches from the egg ; that is, 

 it perforates, by means of a dental apparatus already developed, the 

 larger end of the shell, so as to come into contact with the moistened 

 but still dormant tissue of the axis. 



In this state of things new and important phenomena are 

 exhibited. Under the stimulus of mechanical irritation, or, it may be, 

 of chemical changes set up in the juices of the plant by a specific 

 exudation from the embryonic larvae, many of the cells about the 

 woody axis become endowed with active powers of reproduction. 

 Cell -multiplication thereupon ensues, and the formative tissue, 

 insinuating itself between the anchored ova, gradually surrounds the 

 escaping embryos, until each, embedded in the growing mass, is left 

 sole occupant of its separate chamber. 



In this process, the lowest eggs, or those with longest petioles, 

 are, of course, the first to be overtaken, and, as a necessary con- 

 sequence, their liberated larvae occupy a place nearest the base of the 

 growing gall. Others in turn are successively reached, until, finally, 

 every embryo being embedded, the cellular mass fuses together, 

 and presents to us the characteristic features of the oak-apple gall. 



Here, then, we have a series of facts, both positive and negative, 

 which point to the action of the embryo, and not to the deposit of a 

 special virus by the parent cynips, as the direct and essential agent 

 in the production of the gall. This agent, as will be seen, carries 

 with it all the elements of a vera causa. It is, so far as my observa- 

 tions go, invariably present whenever an oak gall appears ; and, 

 though the exact mode of its operation is, for the present, undeter- 

 mined, it may not unfairly be regarded as sufficient for the effect 

 produced. This is not so with respect to the deposit of a specific 

 virus. Man)^ of the gall-producing insects and acaridae have neither 

 terebra nor poison gland ; and yet, in presence of living ova, hyper- 

 trophy ensues, and a veritable gall appears. 



Granting, for the sake of illustration, the existence and potency of 

 such virus, ought we not, in this case, to expect that, even in the 

 absence of egg or living larvae, the normal energies of the fluid would 

 be exerted, and, in the end, a gall — destitute though it might be of 



