FORMIC ALDEHYDE. 



319 



that the dose of 1 in 10,000, which stops the development of spores 

 for some time, does not suffice to completely disinfect seed-corn, and 

 to pi'event fungi from subsequently attacking the plant. Hecke observed 

 as regards the spores of Ustilago crameri, that they only remained 

 inactive for six to eight days after the treatment, and that the evolu- 

 tion of the disease was only retarded, which delay is often sufficient 

 to guarantee the young plant. The dose of 1 in 1000 suffices, on the 

 other hand, to disinfect the seed completely. 



The following are, moreover, the results of different researches on 

 this subject. 



Mc Alpine has compared the action of blue vitriol, corrosive sublim- 

 ate, and formol on the spores of Tilletia and obtained no infested ears (1) 

 by immersion for one minute in a 2-4 per cent solution of blue vitriol ; 

 (2) by immersion for three minutes in a 0-12 per cent solution of 

 corrosive sublimate ; (3) by immersion for ten minutes in a solution of 

 formic aldehyde 0-05 per cent (0-125 per cent of formaline), whilst the 

 untreated plot gave 95 per cent of rusty ears. These doses thus com- 

 pletely disinfect seed-corn. Moore made the following experiments 

 on oats and obtained : — 



TABLE LXYIL— Showing Effect on Oat Crop of Steeping Seed-Oats in 

 Solutions of Formol of Different Strength and for Ten Mi?iutes up to One 

 Hour. 



Hecke made the curious observation that it sufficed to wash the spores 

 after treatment to redouble all their vigour. Spores of Ustilago crameri 

 steeped fifteen minutes in a formol solution of 0-4 per cent and un- 

 washed, did not germinate in thirty days, but they germinated normally 

 in twelve days if washed after treatment. Treatment with formol 

 even in large doses does not kill the spores if they are afterwards 

 washed with water. The spores of Ustilago crameri are only killed by 

 an immersion of one hour in a 1 per cent bath of formol or three hours 

 in a 0-5 per cent bath of formol. To disinfect seed-corn and sufficiently 

 retard the development of spores, an immersion of fifteen minutes in 

 O'l per cent of formol, of one hour in 02 per cent, and three hours in 

 Q-l per cent suffices. 



Action of Formol on Insects. — Insects withstand formol better 

 than fungi ; coccides are not killed by formol vapour after two days' 

 action (Eeh). Solutions are without action on plant lice (Klein), on the 

 caterpillars of cochylis (Lustner). 



Use. — Oospora scabies, Taxter (potato scab) ; Bhizoctinia Solani 



