CLIMATIC FACTORS 



91 



especially marked by bulb and rhizome geophytes, such as Arum 

 maculatum, Allium ursirium, Leucojum vernum, Scilla bifolia, Tulipa 

 silvestris, Gagea lutea, Muscari botryoides, Ranunculus ficaria, Anemone 

 nemorosa, Adoxa moschatellina. These tender species distinctly show 

 the locally warm conditions under fruit trees in the great Alpine 

 valleys (Rhine valley, Rhone valley, etc.). 



The daily range of temperature in the deciduous forest and the 

 neighboring dry grassland at Bellinchen, on the Oder, is shown by the 

 curves in Fig. 48. 



Temperature and Periodicity. — Attempts to obtain summations 

 of heat from weather bureau data and to relate them to definite life 

 processes of plants — leafing out, flowering, fruiting — have long been 



30°^- 



28 



26 



I 22 

 q5 20 



ex. 



^ 18 



^ 16 



n 



12 

 10^ 



6 8 10 m 

 A.M. 



V 6 

 P.M. 



8 10 



Fig. 48.- 



-Daily temperature range in a deciduous forest (J5) and in a closely adjacent 

 dry grassland (^) in Bellinchen, July 17, 1925. {After Hueck.) 



made. Boussingault (1837) found the sum of the mean temperatures 

 above zero for the duration of the life process of plants under considera- 

 tion. A. P. de Condolle selected for each species of plant a specific 

 zero point for the beginning of his reckoning. Merriam (1898) made 

 summations of temperature from daily means above 6°C. Aside from 

 the fact that these summations should be made from temperatures of 

 the habitat and not from weather bureau records, the very inadequate 

 results of these methods cannot throw much light on the question. 



On the other hand, the so-called phenological charts with curves 

 connecting places where plants are in the same stage of development 

 at the same time express the climate of a region very well and are 

 useful in forestry and agriculture. ^ There is no doubt that the periodic 

 phenomena of vegetation rest fundamentally upon the relation of the 



* The phenological charts of Novak and Simek (1926) for Moravia and Silesia 

 are excellent examples. 



