abstracts: phytopathology 187 



PHYTOPATHOLOGY. — Mechanism of tumor growth in crown gall. 

 Erwin F. Smith. Journ. Agr. Research, 8: 165-186, plates 

 4-65. 1917. 



This paper, with its wealth of illustrations, records the results of a 

 series of experiments testing the effects of various fluids and vapors 

 on plants, undertaken for the purpose of shedding light on the mechan- 

 ism of tumor growth in crown gall. As a result of these studies the 

 author has come to look upon excessive cell proliferation as it occurs 

 in plant neoplasms as due, not to the direct application of stimuli such 

 as endotoxins and other by-products of the growth of the parasite 

 within the host cells, but to their indirect action as the removers of 

 inhibitions. Growth is the normal function of cells but under normal 

 conditions is alwa3^s inhibited beyond a certain point. In the 

 case of neoplasms we have an "inhibition remover that acts locally, dis- 

 turbing tissue equilibriums within limited areas." The author believes, 

 furthermore, that this removal of growth inhibitions is not (or not 

 wholty) due to a chemical action but partly at least to a physical one — ■ 

 viz., a locally increased osmotic pressure produced by the diffusion 

 from the cells of various substances produced within them by the 

 parasite as a result of its metabolism, together with the resultant coun- 

 ter movements of water and food supply, basing this belief upon the 

 researches of Jacques Loeb in artificial parthenogenesis and fertiliza- 

 tion, and on the results of his own experiments. 



The substances produced by Bacterium tumefaciens in culture media 

 containing dextrose, Witte's peptone, calcium carbonate, and water 

 are ammonia, alcohol, acetic acid, formic acid, amines, aldehyde, and 

 acetone. With several of these compounds, the author produced 

 intumescences (both hypertrophic and hyperplasial) without the in- 

 tervention of the organism itself. In addition to obtaining small 

 tumors with crown-gall products (ammonia, dimenthylamine, and acetic 

 acid) the author obtained overgrowths with a great variety of other 

 substances; hence his conclusion that the response must be physi- 

 cal rather than chemical, i.e., due to removal of water from cells, which 

 then divide. 



The plants used were the castor-oil plant (Ricinus communis), to- 

 mato fruits, and cauliflower. The substances tested were injected 

 hypodermically (Ricinus and tomato), placed in tiny open tubes in- 

 serted in the pith cavity (Ricinus, the wound being sealed with col- 

 lodion or adhesive tape), or vaporized in a tight box containing 10.5 

 cubic feet air space in which the plants (cauliflower) were placed for a 



