1898] EECENT PROGBESS IN ROOT-PHYSIOLOGY 385 



The experiments of Koppen have shown that in the case of 

 Zv2nnns albus the radicle ceases to grow at a temperature below 

 7*5° C, and Czapek himself found that at temperatures between 

 0° and 2° C. growth was inhibited in all the plants he used for these 

 experiments. If, therefore, radicles of Lv/phms and Faha were laid 

 horizontally, at temperatures not higher than 2° C, the geotropic 

 curvature was not carried out even after twenty-four hours induction. 

 At the end of this time the still straight roots were placed on a 

 clinostat (an instrument on which gravity is made to act equally in all 

 directions, and on which, therefore, that force is practically eliminated 

 as a stimulating agent) at a temperature of about 19° C, and in 

 from four to five hours geotropic curvatures were clearly visible. 

 In these radicles the perception of the stimulus (gravity) had taken 

 place at the low temperature, althougli the reaction itself could not 

 be accomplished under the circumstances ; for as soon as the 

 temperature was raised, and the conditions rendered suitable for 

 growth, the rootlets carried out a curvature which could only be in 

 response to gravity acting during their stay in the cold, since in the 

 second and warmer stage of the experiment the stimulating action 

 of the force had been eliminated. Although the perception of the 

 stimulus is not entirely inhibited by a low temperature it is none 

 the less affected by it. The lengthened time for which the force of 

 gravity must act to evoke its result, sliows that the perceptive 

 faculty of the living cells of the root-apex is lowered by the lowness 

 of temperature. 



Another condition of environment which was carefully studied 

 was that of an atmosphere containing no oxygen. The work of 

 Kraus, Wortmann, and Correns was the first to give us any infor- 

 mation regarding the effect of absence of oxygen upon geotropic 

 phenomena. These experiments, however, left much still undecided 

 and many points calling for a more extended examination. The 

 time during which these botanists subjected the plant-organs to 

 geotropic induction was not, in any case, sufficiently long to decide 

 with certainty that the stimulation was not felt in the absence of 

 oxygen. A longer period spent in an oxygen-free atmosphere, how- 

 ever, directly affects the life of the root, so that there were great 

 difficulties in the way of obtainiog conclusive evidence. 



The ingenious application of Chudjakow's results by Czapek 

 ■■enabled the latter to overcome the difficulties which had invalidated 

 the work of previous experimenters. Chudjakow, in carrying on his 

 researches on the intra-molecular respiration of vegetable organs, had 

 found as a side-result that the higher the temperature the more 

 rapidly did the organ die in an atmosphere containing no oxygen. 

 It occurred to Czapek to see, therefore, whether a root placed in a 

 vacuum could not resist its usually harmful effect when the tem- 



