u] OF ANTHOCYANINS 19 



on the stems developing in the summer flat leaves whose under side 

 contains abundant anthocyanin, as, for example, Senecio nemorensis 

 and nebrodensis, Valeriana montana and tripteris, Epilobium montanunt, 

 Lactucu muralis, and many others." And again, "That which occurs 

 in plants of the forest shade occurs similarly in those marsh plants 

 whose leaf-like stems or flat, disc-like leaves float on the surface of the 

 water. The green discs of duckweeds (e.g. Lemna polyrrhiza), of the 

 Frogbit (Hydrocliaris morsus-ranw), of the Yillarsia (Villarsia nym- 

 phuidcs), of water lilies (Nymphcca Lotus and thernialis), and of the 

 magnificent Victoria regia, are strikingly bi-coloured, being light-green 

 above and deep violet below." Occasionally anthocyanin is limited 

 to definite areas in the leaf, and in this form is the cause of the dark 

 brown or black spots on leaves (Orchis maculata, Arum maculatum 1 , 

 Medicago maculata, Polygonum Persicaria 2 ), the dark colour being the 

 result of the mixture of purple pigment and green chloroplastids. 



Most of the above examples have been taken from flora of the 

 temperate regions, but when we consider the tropical and sub-tropical 

 regions, cases of red pigmentation are not only more numerous but are 

 also much more striking. It is almost impossible to enumerate the 

 specie which have wonderfully variegated leaves, and constitute the 

 class of 'beautiful-leaved plants' of cultivation. Examples are quoted 

 by Hassack (393) in a paper on variegated leaves, and good plates -have 

 been published in a book by Lowe & Howard (29). A few of the most 

 remarkable are as follows : Calathea, Maranta (Marantaceae), Alocasia, 

 Caladium, Xanthosoma violaceum (Araceae), Tradescantia discolor 

 (Commelinaceae), many Bromeliaceae (Vriesia splendens, Nidularium 

 spp., Billbergia gigantea, Tittandsia), Dracaena spp. (Liliaceae), species 

 of Croton, Acalypha and Codiaeum (Euphorbiaceae), many Gesneriaceae 

 (Sinningia atropurpurea, Episcia sp., Aeschynanthus sp. and Gesneria 

 cinaberina), Coleus Verschaffeltii (Labiatae), Iresine sp., Alternanthera 

 versicolor (Arnarantaceae), Fittonia sp. (Acanthaceae) and numerous 

 Begonias. Hassack points out in a most interesting way how the colour 

 in such leaves may vary from purple or crimson, through brown-reds 



1 In the case of Arum maculatum the leaves are not always spotted ; in fact, according 

 to the evidence of Colgan (73) and of Pethybridge (78), the spotted form is much less 

 common, both in Great Britain and Ireland, than the unspotted. These two authors 

 give some interesting data with regard to the distribution of both forms, as well as obser- 

 vations upon the structure and inheritance of the spot. 



2 Garjeanne (74) mentions the discovery in Polygonum Persicaria of a variegated 

 form in which the chlorophyll is absent from large areas of the leaf, and when this is the 

 case, the anthocyanin patch shows bright red. 



22 



