90 PHYSIOLOGICAL CONDITIONS AND FACTORS [CH. 



synthetic products in the storage tissues of the bulbs, corms, seeds and 

 fruits concerned, from which the chromogen for the pigment can be 

 synthesised, if there is not also already a storage of this substance. 

 But where the supply of chromogen is directly dependent on the photo- 

 synthetic activity of the leaves, darkening of the flower-buds, unless 

 they are already practically mature and supplied with chromogen, 

 prevents or diminishes the formation of anthocyanin. The reddening 

 of leaves and stems where exposed to light may in some way be due to 

 local accumulation of synthetic products, though the direct effect of 

 light is superficially more probable. 



The effect of light in autumnal coloration is even less well explained 

 on this accumulation hypothesis, except that in the last stages of the 

 leaf's existence, photosynthesis must be best carried out in the parts 

 most exposed to light. There is also a general tendency to accumulation 

 of synthetic products owing to low night temperature. 



The formation of anthocyanin in normally uncoloured roots when 

 exposed to light appears to be the most convincing evidence at hand 

 for the production of. anthocyanin due to the direct action of light. 

 Until more evidence has been collected from a number of carefully 

 devised experiments, no definite inference can be drawn. 



In conclusion we may mention some work on more systematic lines 

 which was published by Linsbauer (371) in 1907. He endeavoured 

 to find out the more precise relationships between light and the forma- 

 tion of anthocyanin. For this purpose he used seedlings of Fagopyrum 

 esculenlum which had been grown in the dark and were quite etiolated. 

 Such seedlings were then exposed to light (lamp) of different intensities 

 and for varying lengths of time. From his results Linsbauer concluded 

 that the photo-chemical process of anthocyanin production in light is 

 a typical stimulus reaction, and is dependent upon both the intensity 

 and duration of light. He investigated also the relationship between 

 the times of reaction and presentation, and found it analogous in many 

 respects to that in other stimulus processes, i.e. geotropism, for instance. 

 Whether, however, the appearance of anthocyanin in these seedlings 

 is due to the direct action of light, or to the products of photosynthesis 

 induced by light, cannot be readily ascertained. 



Connection ivith presence of oxygen. 



That oxidation plays a part in the formation of anthocyanin has 

 frequently been suggested. The production of red pigment through 

 the oxidation of a chromogen was the hypothesis brought forward 



