ANNUAL REPORT, 1936 29 



Growth of most species was generally either unaffected or, in some cases, im- 

 proved, as when Rhizoctonia in untreated soils interfered with growth of 

 seedlings. For the present, it is considered safer, however, to delay seeding 

 until at least one day after soil treatment with acetic acid. 



Neither acetic acid nor formaldehyde is always at hand when needed by 

 growers and plantsmen, and this is one principal reason why seeds are often 

 sowed without any protection against soil fungi, for convenience or the lack of 

 it is of course an important consideration in practice. Cider vinegar, as usually 

 sold, contains 4 to 5 percent acetic acid and there are few substances more 

 readily available or more generally at hand. An investigation of its use as a 

 soil disinfectant was therefore begun. 



Five undiluted cider vinegars, 1 containing about 4 to 5 percent acetic acid, 

 were mixed with moderately dry and sandy soils, naturally infested or inoc- 

 ulated, the latter being a more severe test. Seeds were sowed immediately or 

 within 24 hours and soils were then well watered. Vinegar 200, 237 (about %, 

 pint), or 250 cc. 2 usually gave satisfactory but not always complete control 

 of damping-off and it was generally without harmful effect on germination or 

 early growth of most species. In these quantities, it cannot be safely applied 

 to living plants, however. 



Potassium permanganate is occasionally referred to as being a soil disinfec- 

 tant, but in these experiments it did not prevent damping-off of seedlings when 

 added in amounts up to 30 gms. 



Seeds often germinated better in soil to which salicylic acid, 3 to 5 gms., 

 had been applied than in soil without this treatment; but there was no less 

 post-germination damping-off with it than without it. 



Damping-off and Growth of Seedlings and Cuttings of Woody Plants 

 as Affected by Soil Treatments and Modifications of Environment. 



(W. L. Doran.) The time or date of taking cuttings apparently affected their 

 rooting as much as the presence or absence of soil fungi or any other one factor. 

 Fairly hard cuttings of several species lived and struck root as well in rooting 

 media (sand or sand and peat moss) inoculated with species of Pythium or 

 Rhizoctonia as in the absence of these fungi. Cuttings taken earlier or when 

 softer were more susceptible to infection, but when taken too late they struck 

 root more slowly and less well, that is, in smaller percentages. Dates of taking 

 cuttings which rooted well are being recorded, especially in the case of species 

 which are sometimes considered rather difficult to propagate by cuttings ; and 

 some of the information thus'secured should be useful to propagators. 



In studying the effects of several rooting media, it was observed that sand is 

 a better medium for the rooting of hardwood cuttings of Daphne Cneorum than 

 is any mixture of peat moss with sand. 



Acetic acid dusts, made and used as described in connection with the pre- 

 ceding project, were injurious to cuttings inserted within 24 hours after treat- 

 ment of rooting media, although they were safe with the seeds of these same 

 plants. Acetic acid dust and formaldehyde, both of which are soon lost from 

 soil, did not completely protect slowly germinating seeds of woody plants 

 against damping-off. 



Watering of media with much-diluted vinegar did not affect the rooting of 

 cuttings of most species; but the following, which were among the least woody 



'Summarized results of this work have been reported in a previous paper (Science 84: 2177 : 

 273-284. 1936.) 



2 In the report on this and the following project, numbers of cc, gms., or oz. are, except as other- 

 wise indicated, those applied per square foot of soil surface. 



