230 DISEASE IN PLANTS. 



concerned is one of the species of Pythium, the 

 propagation of which is favoured by the rank, 

 over-turgid, and etiolated conditions of the plants. 

 Species of Miicor, Botrytis, and other fungi, may 

 also be met with. 



Bursting of fleshy fruits, such as Tomatoes, 

 Grapes, etc., is due to over-turgescence in rainy 

 weather or excessively moist air. But the pheno- 

 menon is by no means confined to such organs. 

 Hot-house plants when oedematous not infre- 

 quently put out watery blisters from the cortex 

 or leaves, which rupture ; and the stems of fleshy 

 fasciated {e.g. Asparagus) or blanched and forced 

 plants {eg. Celery, Rhubarb) are particularly apt to 

 crack here and there from the pressure of the 

 turgescent tissues on the strained epidermis. 

 Beets, Turnips, and other fleshy roots show the 

 same phenomena in wet seasons. That these 

 ruptures and exposures of watery tissues afford 

 dangerous points of entry for parasites and moulds 

 will be obvious- e.g. Edelfaiile, a rotten condition 

 of the grapes in the Moselle district. 



Root-rot is a common disease in damp, sour 

 clay soils after a continuance of wet weather e.g. 

 Wheat, especially if root-drawn and exposed to 

 thaw water. 



In the disease known as Beet-rot, the roots 

 turn black at the tip, where the tissues shrivel 

 and become grooved and wrinkled extensively. 

 Inside the flesh also blackens and finally rots. 

 In earlier stages, only the vascular bundles are 

 brown and blocked with gum-like substances. 



