6 MASS. EXPERIMENT STATION BULLETIN 351 



Sands had pH values of 5.8 to 6.1 and water-holding capacities of 24 to 27 

 percent. They differed more in degree of fineness, and the poorest growth was 

 most often in the finest sand. This is in agreement with observations of Dunlap; 

 and Biekart and Connors (10) preferred a medium-coarse to a finer sand for the 

 culture of carnations in sand. 



Growth of seedlings of all species was better in sand-sphagnum and sand-peat 

 moss than in sand alone (with usually a little more benefit from the sphagnum), 

 probably because moisture and nutrients were retained better in these media 

 than in sand. Growth was usually as good in sand-sphagnum and sand-peat moss 

 as in soil, and often better. Peat moss increased the water-holding capacity of 

 the sand and lowered its pH value more than did the sphagnum. 



It is evident from the above that sand culture of seedlings controls damping-ofT, 

 but it is perhaps no more convenient to wash sand and apply nutrients once (or 

 more than once, as Dunlap suggests) than it is to disinfect soil chemically. The 

 principal defect of sands — at least of some sands — is that growth of seedlings 

 may be too slow unless nutrient is applied more than once. Seedlings of tuberous- 

 rooted begonias, Ramondia, Primula denticulata and other species grew too 

 slowly in sand to be of a size easy to transplant to better soil when they should 

 have been. There seems to be ample justification for the English horticultural 

 writer (1) who considers sand an ideal medium for germination except for the 

 fact that it requires such vigilant watering (which may mean washing out of 

 nutrient) that it may be necessary to add peat moss to the sand to retain moisture. 



Sphagnum was found no less useful. The sand used in such a mixture should 

 be washed with hot water, and the mixture of sand with peat moss or sphagnum 

 needs nutrient about as much as does sand alone. 



The medium used in the experiments with soil fungicides was a sandy soil 

 made by mixing a sifted compost of sods and manure with sand, half and half 

 by volume. Soils used for seedage of most species ought to be sandy rather than 

 heavier because of the greater risk of the latter's caking and remaining excessively 

 wet too long if overwatered. It is not to be supposed, however, that the proportion 

 of sand in the soil will have much effect on the severity of damping-ofT; and in 

 these experiments, as in those of Gratz (39) and Abdel-Salam (3), damping-off 

 caused by Rhizoctonia was severe in a mixture (half and half) of loam and sand. 

 This was true also when such a soil was inoculated with Pythium. 



There are soils in the trade which have already been sterilized by the firms 

 supplying them, and, unless they later become contaminated, there is little or no 

 damping-off in them. To lessen the cost of using such soil, it was mixed with 

 washed sand up to half and half. No increase in damping-off resulted, and seed- 

 lings grew well without the addition of nutrient up to the stage at which they are 

 commonly transplanted. 



SOIL REACTION AND DAMPING-OFF 



Certain plant diseases are known to be at least partly controllable by adjusting 

 soil reaction. It is, therefore, of interest to learn to what extent such methods 

 might be expected to be effective in the case of damping-off. 



Although investigators are not in complete agreement, it appears from the work 

 of Anderson (6), Jackson (52), and Jones (55) that species of Pythium may cause 

 severe damping-off in soils having pH values of 4.5 or 5.0 to 6.5 or 7.0 and that 

 they may cause some damping-off even in soils with pH values of less than 4.0. 

 That being the case, a soil which is acid enough to inhibit Pythium as a pathogen 

 will probably be too acid for many species of plants. 



