SMITH: CROWN GALL AND OTHER OVERGROWTHS 451 



excessively moist air; by exposure to very dilute 

 vapors of ammonia or of formaldehyd ; by applica- 

 tion of a great variety of soluble substances not 

 the products of parasites, e. g., copper salts; by 

 painting the surface with vaseline and other insolu- 

 ble substances which interfere with the gas exchange; 

 by freezing lightly (Harvey), etc. 



(2) Non-cancerous bacterial tumors — olive knot (due to Bact. 

 savastanoi), beet tumor (due to Bact. beticola). In 

 these the bacteria are abundant and easily seen 

 occupying the vascular bundles and the spaces 

 between cells. Bacterial cavities are produced and 

 the overgrowths are only superficially like crown 

 galls. The secondary tumors are not developed 

 from tumor strands. When the bacteria are intra- 

 cellular the cells are destroyed. 



(2,) Nematode galls. In galls due to Heterodera radicicola giant 

 cells, i. e., several to many nucleate cells, are com- 

 mon. Parasitic nematodes which do not produce 

 galls. Here the anal excretions are voided outside 

 of the plant (Cobb) . Occurrence of several-nucleate 

 cells in crown gall. 



(4) Various fungous galls. Parenchymatic t^5. woody; perish- 



able vs. persistent; witch brooms (see newer work 

 on crown gall). Parenchyma strands (Dodge). 



(5) Insect galls which show features resembling crown galls. 



(a) Galls bearing leaves; galls bearing roots; galls 



bearing modified trichomes. We have now suc- 

 ceeded in producing on internodes by bacterial 

 inoculation crown galls bearing roots, leafy shoots, 

 flower buds, and modified trichomes. 



(b) Galls with cortex carrying bright colors — purple, red, 



yellow. Crown galls produced on pale green balsam 

 stems show a red color in their cortex provided the 

 plants bear colored flowers, but not if they bear 

 white fiowers. The production of red pigment in 

 the cortex has been seen also in axillary (teratoid) 

 crown galls developed on red-flowered Pelargoniums. 

 Etiolation. Excess of chlorophyll. 



(c) Galls opening by opercula— strange but not more 



so than twin-leaf fruits opening in a similar manner, 

 or than a double vascular cylinder in Ricinus with 

 death of intermediate pith and separation into two 

 cylinders. (Jour. Ag. Res. Jan. 29, '17, pi. 37). 



