SOIL TREATMENTS AND SEED GERMINATION 13 



Acetic acid 80 percent, 8 cc. per square foot, and also formaldehyde 7cc., each 

 diluted with 5 times that volume of water, were also applied to (but, of course, 

 not mixed with) soil immediately after seeding. Thus used they were injurious to 

 Felicia, Linanthus, Mathiola bicornis, as well as the species mentioned above, 

 which were uninjured when these quantities of acetic acid or of formaldehyde 

 were mixed with soil before seeding. Pepper, seeds of which germinate slowly, 

 was least injured by these treatments applied after seeding. 



Acetic acid dusts, on the use of which the writer has briefly reported (30), 

 were made by mixing the acid with powdered wood charcoal. Some of the best, 

 containing 23 or 24 percent acetic acid, consisted of 1 pint of 80 percent acetic 

 acid with 2.5 or 2.75 pounds of charcoal, or 1 pint of glacial acetic acid with 3.5 

 pounds of charcoal. These were stored in practically airtight containers and 

 worked into the soil shortly before seeding, at the rate of 1.5 ounces per square 

 foot. Soils were well watered immediately following seeding. 



In soils inoculated with Pythium and Rhizoctonia, germination was improved 

 and the severity of damping-off was lessened by a 15 percent dust, but the control 

 of damping-off was increasingly good when dusts contained 18 to 24 percent 

 acetic acid, with best control by the 23 and 24 percent dusts. 



The relative numbers of plants which lived are recorded in Table 5, which 

 includes the means for several experiments. A 23 percent acetic acid dust also 

 improved germination of Browallia, Cerastium, English daisy, columbine and 

 lupine. 



Table 5. — ^Effect of Acetic Acid Dusts on Final Stands 



The effect of a 23 percent dust in improving stands is also shown in Figure 1. 

 This dust, applied to soil immediately or within 24 hours before seeding, was 

 harmless to the species named in Table 5 and above, and also to rocket, Laburnum, 

 arbor-vitae, onion, Rhododendron calendulaceum , R. catawbieyise, R. carolinianum, 

 and R. Schlippenhachii. Perhaps it would not be harmless to all species, for Alex- 

 ander, Young, and Kiger (5) injured tomato seeds with a 20 percent acetic acid 

 dust, although their carrier was not charcoal but diatomaceous earth and kaolin. 



These acetic acid dusts, as made and used by the writer, were, however, unsafe 

 with cuttings, for even a 17 percent dust, applied to a mixture of sand and peat 

 moss 24 hours before their insertion, injured Ilex, Berberis, Lonicera pileata, 

 Euonymus, Calluna, Chamaecyparis, and Erica. 



Vinegar as usually sold contains 4 to 5 percent of acetic acid and it has occa- 

 sionally been recommended, as by Stafford (82), for the control of damping-off. 

 It is doubtful, however, whether there is much experimental evidence on which 

 to base such recommendations and they usually call for much less vinegar than 

 the writer (30) has found necessary. 



