PART III 



SYNOPSIS OF SELECTED DISEASES 

 I. THE CUCURBIT WILT 



Type. — This is a wide-spread, typically vascular, wound- 

 infection, wilt disease (Figs. 62, 63, 64), transmitted by insects 

 (Figs. 65, 66, 67). The plants wilt suddenly without any visible 

 cause, and on cross-sections of stems of such plants there is a 

 viscid, white bacterial ooze from the vascular bundles (xylem 

 part). The disease is first visible on the leaves locally in the 

 form of dull green, rapidly extending, flabby patches. Later all 

 the leaves wilt and shrivel. It is not known outside of Cucurbit - 

 aceae and some members of this family are not subject. It is 

 believed to be non-tropical in its distribution. Its range toward 

 the equator is unknown. Rand has recently discovered it in 

 the United States as far south as Florida. It occurs in Europe, 

 South Africa, and Japan. In hothouses the disease occurs not 

 infrequently in the winter season, often destructively, and here 

 again insects are the carriers. 



Cause. — It is due to Bacillus tracheiphilus EFS.^ This is a 



1 Note. — The generic names in this book are used by me in the following way : 



Bacillus: A rod-shaped schizomycete, motile by means of peritrichiate fiagella. 



Bacterium: A rod-shaped schizomycete, motile either by means of one polar 

 flagellum or several such fiagella. 



Aplanobacter: A rod-shaped, non-fiagellate, non-motile schizomycete. 



For a discussion of the principles involved in tills nomenclature, see "Nomen- 

 clature and Classifications" in "Bacteria in Relation to Plant Diseases," Vol. I. 



The peptone referred to in this book is Witte's Peptonum siccum. The 

 agar is Kahlbaum's Pulverized Agar Flour. The gelatine is Nelson's Shredded 

 Photographic Gelatine, No. 1. All titrations referred to were made with N/20 

 NaOH, or N/20 HCl, using phenolphthalein as indicator, unless otherwise 

 specified, the merest trace of the pink color being taken as the zero point. 

 Bouillon means 1 per cent peptone-bouillon unless otherwise indicated. Milk 

 means the fresh cream-free product. As already stated in Part II, the color 

 changes in most cases have been compared with Ridgeway's Color Scale {Ri 

 or R2). Sometimes, however, there is no color in Ridgeway's system that fits, 

 and in such cases I have used common terms. 



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