352 



GENERAL PLANT PATHOLOGY 



gum rosin known as ''spruce gum" is collected and sold at from two 

 dollars to two dollars and fifty cents a pound. ^ Where due to the attack 

 of bacteria it is called bacteriosis. Tumescence is the over-turgescence 

 of plant tissues due to the excess of water. It sometimes indicates 

 pathologic changes and was formerly called (edema, or dropsy. Flux 

 is another name applied to the issuance of fluids from wounds in trees, 

 while slime flux issuing from wounds may be frothy, owing to the fer- 

 mentative activity of yeasts and other fungi, which live in such slimes. 

 Manna flux is found in such trees as the manna ash and species of 

 tamarisk. Cuckoo spit is a frothy material found on grasses and 



Fig. 141. — Crown gall with hairy root on nursery stock of Northern Spy apple. 

 - {From Marshall after Paddock.) 



other plants in which green sucking insects live. Honey-dew is the 

 excretion of plant lice, or aphides, and its presence encourages the 

 growth of fungi {Meliola, Scorias). 



13. Rotting. — Rottenness of plant parts is the state of decomposition 

 putrefaction, or decay usually associated with the formation of 

 malodorous, or putrid substances. Several kinds of rots are dis- 

 tinguished as dry rot, soft rot, black rot and gangrene. Usually such 

 rot or gangrene is due to the presence of some bacterial, or fungous 

 organism, which brings about the decomposition of the parts attacked. 

 The decay may be slow, or rapid. Sometimes the rot is associated with 

 the production of bitter substances, as in the bitter rot of apples. 

 ^ Record, Samuel J. : Harvesting the Spruce-gum Crop. Tlie Country Gentle- 

 man, Feb. 26, 1916, p. 475. 



