Physiologie. 307 



depending on the plant considered. Radiation then may be looked 

 upon as the primary causative factor in the cyclic changes. 



The air temperature and wet-bulb depression graphs are very 

 sirailar in form, since the latter can be determined from the former 

 on days in which the absolute humidity of the air is not changing. 

 The transpiration graphs usually rise and always fall in advance 

 of air temperature. 



The evaporation graph from the shallow, blackened tank (water 

 approximately 1 cm. in depth) is similar in form to the graph repre- 

 senting the vertical component of radiation. This is to be expected, 

 since only the vertical component would strike the horizontal waicr 

 surface. The evaporation graph rises and falls with, or slightly 

 later than the vertical component of radiation. 



Computation of the correlation coefficients between transpi- 

 ration and the various environmental factors show the radiation, 

 air-temperature, and wet-bulb depression to be correiated with 

 transpiration approximately to the same degree. The correlation 

 coefficients of transpiration with radiation ränge from 0,82 to 0,89; 

 with temperature from 0,77 to 0,86; and with wet bulb depression 

 from 0,75 to 0,85. These figures show the intercorrelations existing 

 among the environmental factors since the sum of the Squares of 

 the coefficients of independent causative factors influencing transpi- 

 ration can not exceed unity. If radiation is taken as the primary 

 causative factor, the correlation coefficients show that 0,67 to 0,77 

 of the transpiration on clear days under the conditions of these 

 experiments is determined by the radiation intensity. 



If the environmental factors are considered as independent, 

 their relative influence on transpiration may be determined by the 

 method of least Squares. In the case of alfalfa and amaranthus, the 

 vertical component of radiation and the temperature enter inlo the 

 determination of transpiration in the ratio of 1 to 1, approximately^; 

 and the corresponding ratios for vertical radiation and saturation- 

 deficit are approximately the same. On the other band, in the case 

 of rye, the radiation by this method of reduction shows less influence 

 than either temperature or Saturation deficit on the transpiration 

 rate, which from 9 a. m. to 2 p. m. shows a marked departure from 

 the graph indicated by the transpiration during the early morning 

 hours. 



Least-square reductions of the dependence of transpiration upon 

 radiation and air-temperature or upon radiation and saturationdefi- 

 cit do not account entirely for the observed transpiration, although 

 a satisfactor}^ agreement between computed and observed evapora- 

 tion is obtained by the use of these environmental factors. This 

 indicates that the plant undergoes changes during the day which 

 modify its transpiration coefificient. In other words, the writers 

 results Support the conclusion of other investigators that plants 

 under conditions favoring high evaporation do not respond wholly 

 as free evaporating Systems, even if bountifully supplied with water 

 and no visible wilting occurs. M. J. Sirks (VVageningen). 



Ortlepp, K,, Wie wirkt die Ernährung der Tulpenzwiebel 

 auf die Füllungserscheinungen der Blüte? (Zschr. 

 Pflanzenkr. XXVII. p. 114—126. 8 A. 1 T. 1917.) 



Die Ergebnisse der Kulturversuche des Verf. zeigen, dass die 



