For certain early spring flowers, such as Daphne, Galanthns and Hepatica 

 he concluded that Z2>Z3<Z4. 



The last few paragraphs of this paper of Sachs are worth quoting: "If 

 we presume that all numerical values of the above scheme are known, it 

 will be immediately possible to determine, whether a given climate offers 

 the necessary growing conditions for a particular plant. In addition it 

 would be necessary to add the specific time-relations, investigating for each 

 X, y, and z how much time is required to complete phases G, S, V, B and 

 F." 



"Once all these data are known, we can hope that the law can be found, 

 according to which temperature and development of a species are linked. The 

 above scheme only serves to arrange the collected data in a logical manner. 

 Using these known data it would be simple to discover the shortest possible 

 time for development of the plant. This question cannot be answered with- 

 out detailed analysis of the response of the plant, but offers much of interest 

 in physiological respect." 



The work of Blaauw has answered some of the questions asked by 

 Sachs, and has supplied the necessary data for V and B in a number of 

 bulb species. 



All previously mentioned facts show, that in the course of development 

 of a plant there is a succession of processes, each of which may have a dif- 

 ferent temperature range. In some cases these ranges are so far apart, that 

 under constant temperature conditions no continued development is possible, 

 in other cases we find only a shift in optimal temperature from month to 

 month. Such a shift in temperature characteristic can be expected when- 

 ever different processes succeed each other, no matter how short the dura- 

 tion of each process. Thus in photosynthesis the "Blackman" reaction has 

 a Qio of over 2, whereas the light reaction has a Qio of about 1. In photo- 

 periodism Hamner and Bonner (1938) have shown that the dark reaction 

 has a high temperature optimum, whereas the temperature during the photo- 

 period is of secondary importance in flower induction. This shows that the 

 light and dark processes in flower induction can be separated by their tem- 

 perature dependance. In general the photoperiodic response is greatly de- 

 pendent upon temperature, and may be modified or even reversed by ex- 

 treme temperatures {see pages 48-51). 



Whereas in many plants the growth rate stays rather constant from 

 day to night, in others the greater part of stem elongation occurs during 

 night. Therefore, the temperature during night can be expected to have a 

 marked influence on the growth rate of the plant as a whole. During day 

 photosynthesis most likely does not have the same temperature optimum. 



