968 MICROBIAL DISEASES OF PLANTS 



the circulation is impaired, as is shown by the poor growth and dwarfed 

 appearance of the trees. 



The development of this disease is looked upon by Smith* and his 

 associates as paralleling closely what takes place in cancer in man and 

 animals. The primary tumors have been observed to send out "roots" 

 or tumor-strands for some distance into the normal tissue, and from 

 these tumor-strands, secondary tumors may arise which tend to take 

 on the structure of the primary tumor, e.g., "if the latter is in the stem 

 and the former in a leaf, the secondary tumor shows a stem structure." 

 "There are no metastases in crown gall * * * for whether a cancer 

 shall be propagated by floating islands of tissue, or only by tumor- 

 strands, appears to be a secondary matter depending upon the char- 

 acter of the host tissues rather than the nature of the disease." The 

 salient point is the internal stimulus to cell division which arises from 

 the presence of the microorganisms within certain cells. 



METHOD OF INFECTION. Little is known about the natural channels 

 of infection, but inoculation through wounds induced by poor grafting, 

 careless cultivation, and by borers, nematodes, etc., is undoubtedly 

 responsible for many crown galls. 



CAUSAL ORGANISM. Pseudomonas tumefaciens is a short rod with rounded ends, 

 motile by 1-3 polar flagella; measures 1.2 to 2.5/1 by 0.5 to o.Sju; neither spores 

 nor capsules demonstrated; pseudozoogloeae occur; involution forms present; 

 stains with the usual anilin stains; Gram-negative; on agar, slow, four to six days 

 at 25; filiform, raised, white, glistening, somewhat slimy; potato, growth rapid, 

 white, smooth, wet-glistening; gelatin stab, filiform, no liquefaction; moderate, flat, 

 filiform, white, smooth, glistening, no liquefaction; blood serum, moderate; broth, ring 

 or pellicle, clouding absent or inconspicuous; milk, coagulation delayed, curd not 

 peptonized, litmus gradually blued then reduced; silicate jelly, slow white growth; 

 Cohn's solution, scanty or absent; Uschinsky's solution, scanty, not viscid; NaCl 

 bouillon, 4 per cent inhibits, 3 per cent retards; bouillon over chloroform, growth 

 unrestrained; no gas from sugars; ammonia is produced^ nitrates not reduced; indol 

 production small; thermal death-point 51; optimum reaction between +14 and 

 +24 Fuller's scale; opt. temp. 25 to 28, max. 37, min. positive at o; killed 

 readily by drying; moderately sensitive to sunlight; invertase and rennet thought 

 to be produced. 



CONTROL. Thorough inspection of nursery stock and care in the 

 cultivation of orchards "hot to wound the crowns are important factors. 



* Smith, Erw. P., Brown, Nellie A., McCulloch, Lucia, "The Structure and Development of 

 Crown Gall; A Plant Cancer. Bull. 255, Bur. Plant Ind. U. S. Dept. Agric., 1912. 



