VJ21.] 



The Control of Onion Smut. 



445 



After being harrowed flat the land was treated as follows : — 



Plot A ((U scj. yd.) received a mixture of 12 II). of" sulpliiir aiid 24 11). 

 of builder's liuie ; the latter, however, when received, appeared to be 

 completely slaked. Immediately after application the mixture was 

 harrowed in. 



Plot B (28 sq. yd.) received 10 lb, of calcium cyaiiamide worked iu 

 as in Plot A. 



riot C (18 sq. yd.) was treated with a solution of formaldehyde 

 (1 lb. of commercial fornudin dissolved in 3 gal. of water). The solution 

 was applied by means of a watering can. 



In all three eases the seed was sown a fortnight after the land 

 had been treated. The main crop of onions on an adjoining 

 plot acted as a control. 



A considerable amount of disease appeared on all the plots. 

 None of the treatments seemed to have effected any diminution 

 in the intensity of attack. The one interesting fact brought out 

 was the value of thorough surface cultivation. A strip of land, 

 including about four rows along the edge of all the plots, was 

 left unhoed and it was noticed that this strip suffered far more 

 from Smut than did the remainder. This fact has been re- 

 peatedly observed in subsequent experiments. 



Unfortunately, the trials had to be abandoned, and were only 

 resumed when Mr. Mercer and the writer returned from war 

 service in 1919.* 



A further sot of trials was devised in 1919. These trials were 

 based upon three suppositions : — 



(1) That a trial of varieties might reveal differences in susceptibility 

 to attack, which might be turned to account. In the United States, for 

 instance, it has been stated that tender white varieties are more susceptible 

 than are yellow ones.f 



(2) That some means must be discovered of increasing the rate of 

 germination of tlie seed, since once the seedling is above ground it is not 

 susceptible to attack. ^ It was found in the course of laboratory 

 experiments tliat a weak solution of sulphuric acid greatly increased the 

 energy of germination of onion seed, possibly by hydrolysing the starchy 

 endosperm or by rendering the sced-coat more permeable to watery salts. 



(3) That the failure of the forujalin treatment in 1*J15 might be due 

 to the volatile nature of that compound. An attempt was therefore made 

 to increase the length of time during wliich the gas would act by applying 

 solid paraform instead of licpiid formalin. 



* The first lOlD trial was devised conjointly, but as Mr. Mercer left the 

 locality shortly' after the seed was drilled, the responsibility for observations 

 and conclusions rests with the present writer. 

 fB. D. Halstead, New Jersey Sta. Rpt., 181)8. 



T. Wliitehead, On the Life flii^toru <ind Aforphalot/i/ of rmci/sfls cepulo^ 

 Trans. Brit. Myc. Soc.,Vol. vii. pt. I. 1H21, pp. lV)-70." " 



