372 Transactions of the Canadian Institute [vol. ix 



The theory, just stated, furnishes an explanation intended to account 

 only for the stimulation of the protoplasm expressed in cell proliferation, 

 hypertrophy and the production of unusual structures. There are other 

 gall characteristics, however, that can scarcely owe their origin to the 

 action of enzymes alone on the protoplasm of the host. For example, 

 the colour of galls appears to be controlled partly at least by the intensity 

 of the illumination. Thus the galls produced on Salix cordata Muhl. by 

 Pontania pomum Walsh are little, if at all, coloured when the host is grow- 

 ing in deeply shaded stations. Besidas this environmental effect, how- 

 ever, cheri is another factor that may also have an influence on the 

 colour of this gall. De Vries^^ states that the red colour in plants is a dor- 

 mant characteristic in the protoplasm that can be reinstated by stimu- 

 lation. As a distinct confirmation of his view he found that red tints 

 were produced in the leaves of Viburnum opulus L. as a consequence of 

 bruising. This experimeni: seems to be closely paralleled in the sawfly gall 

 Pontania pomum Walsh, where a red colour is apparent in the leaf of Salix 

 cordata Muhl. in a v.iry short time after oviposition. It seems very 

 probable that in this case as in that of Viburnum the dormant red char- 

 acteristic has been reinstated by the mere mechanical injury. It is note- 

 worthy in this connection that shades of red are the predominating tints 

 in gall structures, so that in the production of colour enzymatic action 

 may frequently be operative in reinstating che dormant character red, 

 especially in the case of galls in which che mechanical injury is negligible. 



Further, the shape of the gall and the relation of the various zones 

 to each other are not explainable by reference to any one factor. They 

 doubtless result from a combination of factors. Just what all of these 

 may be is yet not apparent but this much is certain that there appears to 

 be an entire lack of evidence supporting the view that the protoplasm 

 of the host has become endowed with a property that enables it to pro- 

 duce a fairly definitely shaped but withal abnormal structure. Such a pro- 

 nounced change would surely be expressed in the hereditary character- 

 istics, yet there is not a vestige of proof tending to show that insect galls 

 ever produce the slightest variation in the descendants of the host. Not 

 only so, but in the case of stems growing beyond the gall, there is no 

 certainty that the prolongations are abnormal except for the slight 

 dwarfing which is possibly explainable on the basis of an interrupted food 

 supply. Examples of such stems are furnished by Cecidomyia triticoides 

 Walsh on Salix, Chermes abietis Linn, on Picea, or Eurosta solidaginis 

 Fitch on Solidago. Kiister also found in his regeneration experiments 

 that the roots produced from specimens of Pontania salicis were perfectly 

 normal. There is still another argument to be cited in opposition to this 

 view, in the fact that one gall may be parasitic on another. Thus when 



