28 MASS. EXPERIMENT STATION BULLETIN 355 



Milk (bacteria counts) 1,071 



Ice Cream (bacteria counts) 50 



Water 106 



Miscellaneous: 



Streptococci 18 



Throat Swabs 17 



Anaerobes 2 



Smears 2 



Total 1,266 



DEPARTMENT OF BOTANY 



A. Vincent Osmun in Charge 



Effect of Soil Temperature on Gardenia. (L. H. Jones.) Under the title "Rela- 

 tion of Soil Temperature to Chlorosis of Gardenia," previous work has been pub- 

 lished in Jour. Agr. Research 57:611-621 (1938). Recent results show that low 

 soil temperatures definitely favor the initiation of reproductive development and 

 that high soil temperatures favor vegetative development. Bud development 

 and blossoming are normal as soil temperature is raised, but abnormal if it is 

 lowered. Bud drop is a sinister threat to successful commercial culture of garden- 

 ias. The sudden dropping of buds appears to be closely related to previous condi- 

 tions rather than to conditions prevalent at the time of falling. Neither an in- 

 crease nor a decrease in soil temperature prevented well-developed buds from 

 falling from plants that were chlorotic and hard. 



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

 O'Brien. Cooperative with Chemistry.) The fact that rate of growth, size 

 of leaf, and healthy green color of the gardenia plant are affected by the root 

 temperature raises the question of what precise factors are involved. Since 

 temperature governs the speed of reaction and is not of itself the reaction, it is 

 of importance to study the effect of temperatures on all known reactions con- 

 cerned with root activity. For the present, it is deemed advisable to simplify 

 the problem by using nutrient solution culture of plants instead of a complex 

 soil environment for the roots. 



Time has been spent in perfecting a technique, in which soybean plants are 

 used. It is now possible to control the temperature of the solution in which the 

 roots are kept. The solution temperatures used are 50°, 70°, and 90° F. Pre- 

 liminary results indicate that root temperature affects the rate of transpiration 

 and absorption of water. Plants in a nutrient solution at the low temperature 

 wilted, thus definitely showing the depressing effect of low root temperature on 

 absorption of water. At the higher solution temperatures, the rate of change of 

 the pH value of the solution increased, this increase also being attributable to 

 absorption activity. It will be of considerable interest to learn whether there are 

 different temperature levels at which all nutrients may be absorbed and trans- 

 located, or whether each element may require a different temperature level. 



Soilless Plant Culture. (L. H. Jones.) Considerable time has been given to 

 problems arising from a popular interest in growing plants in water or sand sup- 

 plied with inorganic nutrient elements. From conferences and correspondence, 

 it was learned that improper use of chemicals and the purchase of wrong chemicals 

 were the causes of most failures. In particular, mistakes were made in obtaining 

 potassium phosphate, which should be monobasic (KH., PO4), and iron sulfate, 



