1887-88.] Colouring Matters of Leaves and Flowers. 287 



or more shaded ; but it is worthy of attention that this 

 change is not in one direction only. Shaded parts may 

 at times be more green, at times less green, than are parts 

 exposed to more light. Thus strong light has been shown 

 by Pringsheim to be injurious, as it quickly destroys the 

 xanthophyll and the chlorophyll when very intense. 

 Batalin showed in this connection that by very strong light 

 the green colour might be made to disappear from branches 

 of Coniferae (this without modification of the protoplasmic 

 corpuscle), and that after a few days yellow again appeared 

 in the corpuscles ; he was able, indeed, to induce this change 

 in the same branch several times in the course of a summer. 



Light appears to affect the production of the fluid colours 

 which riahault regards as the less stable compounds, such 

 as reds and many yellows. Askenasy and later Flahault 

 point out that tliis is in opposition to the observation of 

 Sachs, who had doubtless experimented on a very limited 

 number of flowers, and who held that, provided a sufficient 

 supply of nutriment were accessible to the plant, it would 

 colour its flowers as well in complete darkness as in 

 daylight. 



As before noticed, the less stable yellow phycoxanthine 

 will disappear in strong light somewhat rapidly ; whilst the 

 red, according to Vines, and the yellow, according to 

 Flahault, are found in less proportion in relatively weak 

 light. These colours seem to alter most readily, as indeed 

 we should expect from their suspension in the cell-sap, and 

 they indicate clearly to us that a mean amount of light is 

 most advantageous to their production. 



Light appears to effect colour-change in certain green 

 parts of various plants by acting upon the protoplasm which 

 surrounds the chloroplasts, as Sachs has shown, producing 

 a deeper shade when the chloroplasts are aggregated, as they 

 are by day, on cell-walls at right angles to the direction of 

 incidence. 



(^) Of indirect effects we have from a longer exposure to 

 light an increase in the reserve material assimilated ; this 

 allows of the production of brighter flowers, more material 

 being at the disposal of those processes of metabolism which 

 produce colour. We have also such indirect influences as 

 may be exerted by the production of alkaloids, organic acids, 



