What is a Vegetable Gall? 5 



has special reference to the point now in review : " What 

 are commonly known as galls are vegetable deformities or 

 excrescences due to parenchymatous hypertrophy. The 

 exciting cause of the hypertrophy, in the case of the typical 

 galls, appears to be a minute quantity of some irritating fluid, 

 or virus, secreted by the female insect, and deposited with her 

 egg in the puncture made by her ovipositor in the cortical or 

 foliaceous parts of the plant. This virus causes the rapid 

 enlargement and subdivision of the cells affected by it, so as 

 to form the tissues of the galls. Oval or larval irritation also 

 without doubt plays an important part in the formation of 

 many galls. Though a certain relation is necessary between 

 the 'stimulus' and the 'supporter of the stimulus,' as evidenced 

 by the limitations in the majority of cases of each species of 

 gall-insect to some one vegetable structure, still, it must be 

 the quality of the irritant of the tissue, rather than the specific 

 peculiarities of the part of the plant affected, that principally 

 determines the nature of the gall." 



Other English writers might be cited, but to multiply 

 quotations would be but to reiterate the same ideas. The 

 opinions of French and German writers on the subject of gall 

 formation are identical. 



These opinions only concern galls directly due to insect 

 agency. The researches during the past few years in the 

 department of agricultural zoology show us that many galls 

 are due to the presence of nematoid worms within the tissues 

 of the plants, and not only are they present upon the aerial 

 portions of the plants, but are numerously disposed upon and 

 within the roots. This latter fact — viz. the presence of galls on 

 roots — does not appear to have been known to any of the early 

 writers. This, however, is not the only agency unsuspected 

 until recently. Various forms of fungi are now known to attack 

 several parts of trees, and arc especially destructive to the fruits 

 of the Frunus order. Some of the lower orders of plants also 

 are considerably swollen, distorted, and their functions rendered ■ 

 abortive, by the same cause. The boughs of fir-, beech-, ash-, and 

 oak-trees are affected by fungi, and enormous gall-growths are 

 oftentimes the result ; while the semi-e.xposed roots of ash- and 

 birch-trees have been found distorted and swollen in a similar 

 manner. 



