312 
PATHOLOGY: E. F. SMITH 
This conception of dominance of linked factors to account for the facts 
as so far known does not preclude the possibility of a physiological effect 
resulting from hybridization apart from hereditary factors if such an 
effect can be demonstrated. It simply coordinates the existing knowl- 
edge of heredity to give a comprehensible view of the way in which 
heterosis may be brought about. 
^ Contribution from the Connecticut Agricultural Experiment Station and the Bussey 
Institution of Harvard University. 
2 East, E. M., Connecticut Agric. Exp. Sta. Rep., 1907, 1908, (419-428); Amer. Nat., Lan- 
caster, Pa., 43, 1909, (173-181). 
^Shull, G. H., Amer. Breeders Assoc. Rep. 4, 1908, (296-301); Atner. Nat., Lancaster, 
Pa., 45, 1911, (234-252). 
*East, E. M., and Hayes, H. K., U. S. Dept. Agric, Bur. Plant Ind. Bull. No. 243, 1912. 
5 Keeble, F., and Pellew, C, /. Genetics, Cambridge, 1, 1910, (47-56). 
CHEMICALLY INDUCED CROWNGALLS 
By Erwin F. Smith 
UNITED STATES DEPARTMENT OF AGRICULTURE 
Communicated. January 26, 1917 
In 1911 in Bulletin 213 on "Crown Gall of Plants: its Cause and 
Remedy" (Bureau of Plant Industry, U. S. Dept. of Agric.) I expressed 
the conviction that while the disease was clearly due to Bacterium tume- 
faciens we would eventually be able to go a step farther (I.e., p. 175) 
and determine just what by-products of the organism were the direct 
cause of the over-growth. With this end in view, on several occasions 
I prepared flask cultures of the organism for use of the chemist of the 
Department and with substances said by him to be present in the cul- 
ture flasks and absent from the controls I have recently made ex- 
periments which tend to confirm my earlier supposition and expectation. 
It is not maintained for a moment that these are the only substances 
that are able to cause overgrowths in plants but only that they are the 
most interesting ones in that they are the products of a cancer parasite, 
or, if one prefers so to express it, of a schizomycete which is the cause 
of a plant tumor possessing many features in common with animal 
cancers. 
The substances produced by Bacterium tumefaciens in very simple 
culture media, i.e., in flasks of distilled water containing 1% dextrose 
and 1% peptone with a little calcium carbonate added to neutralize 
any acids formed and thus to favor long continued growth since the 
crown gall organism is very sensitive to its own acid products, are — aide- 
