vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 89 



anthocyanin formed in the dark, the following examples may be 

 quoted : 



Leaves of Beta (Morren). 



Seedlings of Phalaris and Secale (Hallier, 272). 



Intense rose-red coleoptile in Secale (Gertz, 19). 



Red coloration in shoots of Opuntia robusta and 0. leucotricha. 



Spots on leaf of Orchis latifolia (Gertz, 19). 



Red- veined leaves of Crepis paludosa (Gertz, 19). 



Faint reddening in stolons of Solanum tuberosum (Gertz, 19; Sachs, 

 269). 



On the other hand innumerable cases may be quoted in which light 

 appears necessary for the formation of the pigment: 



Reddening of seedlings is entirely absent in the dark in Polygonum 

 tartaricum, Celosia, Beta (Weretennikow, 273). This has been confirmed 

 by Schell (285) for seedlings of Polygonum, Rumex, Rheum and Amaran- 

 thus and by Batalin (293) for Fagopyrum. The most casual observation 

 will also afford instances of cases where anthocyanin is developed on 

 the sides of stems, twigs and petioles which are exposed to the sun, 

 the opposite side remaining green 1 . Such phenomena are specially 

 mentioned in stems of Cornus sanguinea, C. sibirica, species of Tilia, 

 Rosa and Rubus (Gertz, 19), of Cuscuta (Mirande, 332), of Helianthus, 

 Crataegus and stolons of Fragaria (Dufour, 305). 



The development of autumnal coloration often only takes place 

 in the parts of leaves and stems exposed to light, as was noted long 

 ago in Viburnum Lantana (Voigt, 264) and Rhus Coriaria (Macaire 

 Princep, 3). Gertz (19) also points out that, in Viburnum Opulus, 

 V. Lantana, Cornus sanguinea, C. sibirica and Prunus Padus, the 

 autumnal leaves may show quite clear natural photographs of the 

 leaves covering them, because anthocyanin is absent from the covered 

 surface. Similar lines and spots may be observed in winter-reddened 

 leaves (Silene, Viscaria, Armeria, Hieracium, Pilosella). 



Development of pigment in roots exposed to light has been observed 

 in Salix (Hallier, 272 ; Schell, 287) and Zea (Dufour 305 ; Devaux, 308). 



It is difficult to draw conclusions from the rather conflicting state- 

 ments given above. One fact stands out definitely, namely, that 

 absence of light itself is no bar to the formation of anthocyanin in many 

 cases, such as the root of Beta and the flowers of Tulipa and 7m. But 

 in the majority of such cases there is obviously a plentiful supply of 



1 It has been noted by Parkin (77) that the under surface of leaves is more sensitive 

 to light and reddens more easily than the upper. 



