[Vol. 2 



538 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



but this is readily accounted for by the exposure of its roots 

 to the atmosphere of the laboratory for 30 minutes, a condition 

 noted in other cases above. 



Cultures 9 and 10 of this series, the results from which are 

 not represented because both tops and roots were killed out- 

 right, the resulting exosmosis therefore being immediate and 

 high (x being about 88.0 cm.), were exposed for 15 and 33 

 minutes respectively to a temperature of — 6.5° C, the roots 

 being out of the medium. In a very short time, on returning 

 them to the laboratory, the tops wilted and drooped over the 

 supporting wires and the roots became very flaccid. In the 

 case of No. 11, however, an interesting gradation or interme- 

 diate condition was observed between it and Nos. 9 and 10 on 

 one hand and between it and the controls on the other. While 

 the tops in No. 11 wilted and drooped somewhat soon after 

 being returned to the higher temperature of the laboratory, 

 they did not become entirely limp and the roots were only 

 slightly less turgid than those of the controls. Even after 4 

 days the tops of No. 11 were not drooping much, though the 

 tips of the branches and the upper leaves were dead ; the lower 

 part of the stems and the lower leaves remained green and 

 normal. The lateral roots and the older part of the main 

 roots remained nearly normal, but the tips of the latter were 

 flaccid and shrunken for about 2 inches. Culture 15 showed a 

 very slight flaccidity in the tops and roots soon after the treat- 

 ment, and after 4 days some of the younger leaves and the tips 

 of the older leaves were blackened, curled, and dried some- 

 what, but the great part of the tops remained normal in ap- 

 pearance ; the roots were slightly flaccid at the tips, but were 

 in general practically normal. Cultures 12, 13, 14, 16 and 17 

 were normal in respect to both roots and tops. 



The interval between 15 and 30 minutes is shown in fig. 9 

 to be the critical period for the pea plants exposed in a 

 tumbler to a temperature of from — 2°C. to — 2.5°C, for an 

 exposure of 30 minutes caused considerable exosmosis, while 

 one of 15 minutes srave a curve armroximatelv that for normal 



plants. 



ast the effects of low and high temperatures, Nos 



