22 MASS. EXPERIMENT STATION BULLETIN 369 



in the maximum effect that air temperature has on soil temperature. 



Some attention has been given to the theory that soil temperature is not in 

 itself a direct factor, but is a governing agent that controls other factors. Spraying 

 chlorotic leaves with an iron solution (5 percent ferrous sulfate) has produced 

 spotted leaves with irregular areas of dark green surrounded by the general 

 chlorotic field. This would indicate that soil temperature either alters the ab- 

 sorption of iron or affects the root system so that, even if the iron is absorbed, it 

 cannot be translocated to the leaves. There is also the fact that growth can be 

 not only slowed down, but actually stopped by low soil temperatures. There is, 

 therefore, cumulative evidence that nutrient absorption and nutrient transloca- 

 tion, either or both, may be governed by soil temperature. 



Root Temperature Effects in a Nutrient Solution. (L. H. Jones and G. E. 

 O'Brien. Cooperative with Chemistry.) Soybean plants of the Manchu variety 

 were grown in three-salt nutrient solutions maintained at the three thermo- 

 statically controlled temperatures of 50°, 70°, and 90° F. Since the air tem- 

 perature about the plants was the same, the differences in the amount of water 

 transpired and nitrogen absorbed were due to the root temperature environment. 



The results showed that the quick lowering of the root temperature from about 

 70° to 50° F. caused the plants to wilt. Transpiration and nitrate absorption 

 were lowest at 50° F. The figures on nitrate absorption indicated that the op- 

 timum root temperature was 70° F. or higher, but less than 90° F. No relationship 

 could be established between the amount of water transpired and the amount 

 of nitrogen absorbed. It is evident that the availability of water as influenced 

 by root temperature can alter the rate of transpiration, a factor which is in- 

 dependent of the evaporating power of the air. The investigation confirms other 

 reports that the amount of solutes, in this case nitrogen, enters the plant in- 

 dependently of the amount of water transpired. 



Plant Containers. (L. H. Jones.) Fuchsia and heliotrope have proved to be 

 excellent plants as indicators in various types of plant containers. Fuchsia has a 

 characteristic red midvein when nitrogen deficient. When nitrogen is applied, 

 the first noticeable response is the disappearance of the red vein. This has taken 

 place in a time period of 6 days. It may be detected more readily than a change 

 in the greening of yellow-green leaves. Heliotrope in porous clay flower pots 

 develops a matted root system against the wall of the flower pot as shown in the 

 photograph on page 51. Since this response is due to the accumulation of nutrients 

 in this region, the thickness of the mat indicates the zones of fertility in the soil. 

 This mat of roots also may be used to demonstrate the necessity of keeping the 

 pot wall moist in order to protect these feeding roots from drought. 



Study of Diseases of Ornamental Herbaceous Plants Caused by Soil-Infesting 

 Organisms, with Particular Attention to Control Measures. (W. L. Doran.) 

 Damping-off was well controlled by subirrigation, when the pots oi flats of soil, 

 after seeding, were set in shallow pans of solutions until the soil was saturated. 

 Results were better with vinegar or formaldehyde (1.5 quarts or 3 to 4 teaspoon- 

 fuls, respectively, per gallon) than with formic acid or pyroligneous acid as used. 

 If soil is too wet before treatment, formaldehyde is to be preferred to vinegar, 

 as it is also with very small seeds which may be injured by the growth of mold 

 on the soil following the use of vinegar. With the.se exceptions, vinegar gave as 

 good control as did formaldehyde. Formaldehyde, thus applied, was more 

 effective in soils which, before treatment, were not more than 25 percent sat- 

 urated than in soils which were already 50 percent saturated. It may take 

 longer, however, to subirrigate a completely dry soil, and there was injury to 

 some species by 4 cc. formaldehyde in such soil. 



