88 PHYSIOLOGICAL CONDITIONS AND FACTORS [CH. 



in a dark chamber certain shoots or branches only, the other parts of 

 the plant being in the light. Of plants grown entirely in the dark, 

 Sachs (269) was able to distinguish two classes : (a) flowers which develop 

 colour normally in the dark without being previously exposed to light 

 (Tulipa, Iris, Hyacinthus, Crocus); (b) flowers which only develop 

 colour in the dark if the buds have been fully exposed to light until 

 just before opening (Brassica, Tropaeolum, Papaver, Cucurbita). Of 

 Tulipa Gesneriana Sachs specially remarks : " Die schon gefarbten und 

 normal entfalteten Bliithen auf den etiolirten Pflanzen machten einen 

 hochst sonderbaren Eindruck." And of Iris pumila he says: "der 

 zart hellblauliche Grundton der Perigonzipfel, die dunkelviolette 

 Aderung, welche gegen den Grand der Zipfel bin in das blaulich Pur- 

 purescirende iibergeht, das Orangegelb der Barte, das schon warme 

 Blau der Narben und die himmelblaue Farbung des Pollens, alle diese 

 Farbungen waren bei der Bliithe der etiolirten Pflanze eher glanzender 

 und gesattigter als bei den am Lichte entfalteten." In the case of 

 Tropaeolum, Papaver, etc., if the plants were darkened just before the 

 buds unfolded, normally coloured flowers were produced, but later 

 buds develop flowers with decreasing amounts of pigment. In the 

 cases where shoots only were darkened, the flowers borne upon them 

 were normal as regards size, but the coloration was less intense. Further 

 experiments were made by Askenasy (282) who confirmed Sachs' 

 results for Tulipa and Crocus, though he found Hyacinthus flowers 

 rather less coloured in the dark. Other plants (Pulmonaria, Antirrhinum 

 Silene, Prunella) showed less production of anthocyanin in the dark 

 if the buds had not been previously exposed to light; in Prunella, 

 almost white flowers were formed. Sorby (144), Beulaygue (339), Gertz 

 (19) and others have confirmed these results for the flowers of various 

 species, showing that considerably less, very little, or no colouring 

 matter at all, is formed in the dark. 



As regards coloration of fruits, observations do not entirely agree. 

 Senebier notes that apples do not redden unless exposed directly to 

 light. However, as pointed out by Gertz, the reddening of apples is 

 more or less accessory, but in fruits of which anthocyanin production 

 is a distinguishing feature (Crataegus, Rosa, Sambucus), Askenasy (282) 

 found by partial darkening when green, the pigment developed equally 

 well in both illuminated and darkened parts. Both Laurent (315) 

 and Miiller-Thurgau (298) agree that the coloration of grapes can take 

 place in the dark. 



In purely vegetative organs observations are more conflicting. Of 



