CLIMATIC FACTORS 



99 



The effect of light upon eonstruciive metabolism and storage 

 in plants is conclusively set forth in the work of ZolHkofer (1919). 

 Storage and dissolution of starch are dependent on light stimuli. 

 The formation of alkaloids seems also to be greatly influenced by light . 

 A close relationship has likewise been established between the flowering 

 of undergrowth species and the light intensity within deciduous 

 forests (Fig. 53). 



Formation of Chlorophyll. — The relation of light to the formation 

 of chlorophyll is better understood. At low intensities there is a 

 definite relation between amount of light and production of chlorophyll. 

 At high intensities the chlorophyll content becomes less. 



On this account the leaves of plants of alpine meadows, exposed to 

 strong light, contain considerably less chlorophyll than leaves of the 

 same species from lower altitudes. On the other hand, the snow- 



30 ^ 



Jan. Feb. Mar. Apr May June July Aug. 5epf. Oct Nov. Dec. 



Fig. 5,3. — Seasonal flowering and light relations within the beech forest of Slovakia. 

 .4, Light inten.sity; B, number of species in flower. {After Mikyska.) 



pocket plants of alpine heights, which during a large part of the year 

 produce leaves underneath the snow, have abundant chlorophyll 

 (Henrici, 1918). 



Germination of Seeds. — ^The effect of light upon germination is 

 due to photic and chemical stimuli within the seed. This has recently 

 been investigated by a number of workers {e.g., Cieslar, Figdor, 

 Gassner, Kinzel, Lehmann). According to the predisposition of the 

 seed, light may accelerate or retard germination. Seeds of Elatine 

 alsinastrum may lie for years in the dark without germinating, whereas 

 on exposure to light they germinate 100 per cent in 18 days. 



In contrast to this "light germinator," Nigella saliva, a pronounced 

 "dark germinator," will not germinate at all in light but will germinate 

 100 per cent after a few days in the dark (Kinzel, 1915). 



The seeds of Lythrum, salicaria, totally unable to germinate in 

 darkness, will sprout after a very short illumination. The speed of 



