, DISKASES OF MAXGKLS AND BEET 105 



\ 



youno-est being- free. Differs from leaf spot in 

 that the whole leaf surface turns brown, and 

 thickens. 



Cause, — Investigation has shown that on and 

 within the surface of the brown parts the mycelium 

 of .V. putrefaciens may be formed. Trom this 

 mycelium brown hypha- arise, bearing- at the ends 

 large pear-shaped septate spores, which are very 

 easily detached and carried by the wind. A germ 

 tube grows from each of the chambers. 



Pi'eventive Measures. — 



1. Remove the leaves of attacked crops. 



2. .Steep the seed in formaldehyde solution (see 



p. 32)- 



i\^ Leaf Rust i^Uromyces Bctcr, Tulasne). 



Class: Teliosporpie ; Order: Ureimnales. 



This disease is seen on both mangels and sugar 

 beet, especially in those fields where they are grown 

 many years in succession. Damage is not serious. 



Symptoms. — Appears on leaves late in the season 

 in the form of small yellow^ish pustules, the re- 

 mainder of the leaf remaining a healthy green, unless 

 the spots are exceedingly numerous, in which case 

 it turns a sickly colour. It is chiefly the older leaves 

 that are attacked. 



Canse^ — ^The disease is due to Uromyces BetcF. 

 The pustules on the leaf consist of uredospores of 

 the fungus ; these are blown to healthy plants, there 

 setting up new centres of disease. 



