SOME OF THE PESTS AND DISEASES 131 



become an exceedingly serious matter to all lovers of the 

 Sweet Pea. No one appears to know what to do with 

 plants affected by this dreaded scourge. Until informa- 

 tion of a reliable kind is forthcoming, and this from an 

 undoubted authority, it were better to pull up affected 

 plants and burn them forthwith. In this way the disease 

 may be stamped out. It would be sheer folly to allow 

 such plants to remain in any collection after the disease 

 has been determined by the grower. 



Mr George Massee, of the Royal Botanic Gardens, 

 Kew, says the disease is of a physiological nature. One 

 feature common to all plants suffering from "Streak" 

 is the rarity, or often the total absence, of nodules on 

 the roots. He says, in the "Sweet Pea Annual" for 

 1909, " This is due to the nitrogen-fixing bacteria being 

 rendered inert, or doing work of a nature detrimental 

 to the pea plant, by the excess of nitrogenous manure 

 used." An excess of manure has usually a deleterious 

 effect on the soil, and on the organisms present, the 

 result being " Streak " in the plants. We may, there- 

 fore, overdo the manuring of Sweet Pea quarters. 



