LOW GRADU NITROGENOUS MATERIALS, ETC. 69 



with oats and wheat. When the season is especially favorable 

 to the production of nitrates in the soil during the growing period 

 or when oats and wheat are grown on rich nitrogenous soils rust 

 is more prevalent than usual. Plant diseases due to excessive 

 nitrogen are perhaps more noticeable with crops grown under 

 glass than outside. Most of the soils that are used in hothouses 

 are very rich in nitrogen and the high temperatures kept renders 

 nitrification very rapid. The color of the leaves of hothouse 

 crops becomes a darker green when excessive nitrogen is present ; 

 the leaves become tender and thin and seem to be easily attacked 

 by certain fungi unless extra precautions are taken. Cucum- 

 bers are especially susceptible to disease in the presence of ex- 

 cessive nitrogen. 



