452 BROOKLYN BOTANIC GARDEN MEMOIRS 



(d) Galls with very definite and distinct strata of gall 

 tissue — parenchymatic, vascular and protective, 

 e. g., cynipid galls. Kiister's prosoplasmatic galls. 

 Many insect galls differ from crown galls in that 

 (i) the parasites are few or reduced to a single 

 organism, and (2) are extracellular, whereas in crown 

 gall the parasites are more numerous and are intra- 

 cellular. Many differences in structure, even of the 

 more complex galls, can be explained, I think, 

 by these two dififerences, especially if we assume 

 (3) that the kind of reaction depends on the volume, 

 direction, and velocity of the stimulus, its constant 

 or intermittent flow, and on location, distance, 

 and mobility or immobility of the source of the 

 stimulus. As in various insect galls so in crown 

 t galls, there is a tendency toward the production 

 of more primitive tissues and of various anomalously 

 formed organs. 

 III. Crown galls are formed by extrusion of chemical substances. I have 

 recently produced galls with diluted crown-gall products and 

 this, it seems to me, suggests a new method of attacking gall 

 problems in general, especially those in which the gall para- 

 sites can be cultivated pure in sufficient quantity for chemical 

 analysis, e. g., various fungi. Striking results have been ob- 

 tained but many tests are yet to be made with the crown-gall 

 substances in various dilutions, mixed and separate on a variety 

 of tissues of responsive ages. Various types of cell growths 

 have been produced by the action of am.monia, acetic acid, 

 formic acid, aldehyd, etc. (all products of Bacterium tumefaciens , 

 the crown-gall organism) in less than killing doses, that is, 

 various degrees of hypertrophy and hyperplasia of cells and 

 mixtures of the two have been observed. Sometimes theie is 

 great stretching of cells as in certain fungous and insect galls. 

 Giant cells in the animal pathologist's sense of that word, 

 namely, cells containing several to many nuclei, such as occur 

 in the common nematode galls, are to be searched for in all 

 sorts of plant galls and to be produced, if possible, experi- 

 mentally, i. e., with gall-forming substances. In due time we 

 shall be able, I believe, to get these multinucleate cells at will. 

 Probably they are weakened cells. Two very important things 

 to be determined are whether the size of the cell depends on 

 the volume or rate of movement of the stimulus or on the 

 kind of stimulus, and whether mixed stimuli applied in varying 

 proportions change the manner of cell reaction. 



