388 



GENERAL PLANT PATHOLOGY 



within the tumor cells as the result of the meUbolism of the im- 

 prisoned bacteria (Psetidomonas tumefaciens). Growth of the tumor 

 comes about not by the direct application of stimuli, but indirectly 

 by the removal of various inhibitions. Under normal conditions the 

 physiologic brakes are on at all times, more or less, in both plants 

 and animals, and only when they are entirely or largely removed in 





^l^*"M^^^i2 



Fig. 155. — Cross-section of one lobe of tubercle of Lupinus anguslifolius, con- 

 taining bacteria, X circa 60. (After Moore, Geo. T., Yearbook U. S. Dept. Agric, 

 pi. xxxviii, 1902.) 



particular areas do we observe an unlimited cell proliferation result- 

 ing in the hasty and peculiar growths known as neoplasms, or cancers 

 (Figs. 158, 159). Various weak (dilute) poisons are known to cause 

 cell proliferations in plants — that is, copper salts, ammonia, salts of 

 lithium, and the excretions of the larvae of gall flies, of certain nema- 

 todes and of various fungi.' 



The true fungi (EUMYCETES), including all the important groups, 

 'Smith, Erwin F.: Mechanism of Tumor Growth in Crown gall. Journ. Agric. 

 Res. viii: 165-186, Jan. 29, 1917, with 65 plates. 



