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. 
savastanot), 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. 
3) Nematode galls. In galls due to Heterodera radicicola giant 
cells, 7. 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 vs. 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 flowers. 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, pl. 37). 
