20 THE MORPHOLOGICAL DISTRIBUTION [en. 



to browns and bronze-greens, according to the amount of anthocyanin 

 present, and its situation in the leaf, whether epidermal or deep-seated. 



Stahl (405) lays great emphasis on the fact that many of these 

 variegated-leaved plants, and those with purple and red under-surfaces, 

 inhabit in the tropics, as in the temperate zones, the damp and shady 

 forest regions; he quotes examples of such in support of his views 

 upon the physiological significance of anthocyanin, to which we shall 

 return in Chapter vm. He notes that the orders specially represented 

 are Araceae, Marantaceae, Piperaceae, Begoniaceae, Melastomaceae, 

 Orchidaceae (Pogonia crispa) and Vitaceae (Cissus discolor) ; these 

 probably include many of the plants already mentioned above. Some 

 of these shade-loving plants are, in addition, characterised by a velvety 

 surface due to epidermal papillae, which emphasises the richness of 

 the variegation colour. Spotting and flecking with 'anthocyanin are 

 also common in tropical plants, and occur on a much larger scale than 

 in the temperate zones; instances are given by Hassack (393) and 

 Stahl (405), such as Gesneria cinaberina, Tradescantia zebrina, Musa 

 zebrina Van Houtte and Costus zebrinus. 



Although the observations, which led Stahl to conclude that antho- 

 cyanin development is a characteristic of many shade-loving plants, 

 are undoubtedly correct, yet it is also true that when a plant is capable 

 of foaming anthocyanin, those individuals which inhabit dry and sunny 

 situations develop more anthocyanin than other individuals in moist 

 and shady positions. That is, a plant may be green-leaved in the 

 shade, and more or less red-leaved when exposed to the sun. This 

 fact is at once patent to any one who gives attention to the matter, 

 as the observations of F. Grace Smith (412) have shown. This author 

 examined plants from regions in Massachusetts and Maine, and of 285 

 plants showing anthocyanin, 150 were from dry sunny places, 61 from 

 dry shady places, 40 from wet sunny places and 34 from wet shady 

 places. It seems likely that the phenomenon of pigmentation in shade, 

 especially in the tropics, is a special adaptation, and of a different nature 

 from the more general reddening of vegetation in sunny situations, 

 and that some explanation may be found for the apparent contradiction 

 between the two phenomena. Though F. G. Smith's observations do 

 not give sufficient information to be conclusive, there is one significant 

 fact among them, namely, that in wet shady places, the percentage of 

 cases of red colour in the leaves is higher than that in the stems, whereas 

 among the plants as a whole, anthocyanin was more frequently found 

 in steins and petioles than in leaves. This may indicate that reddening 



