138 THE SIGNIFICANCE OF ANTHOCYANINS [CH. 



and the intensity of the latter when present, reach a minimum. 

 The vegetation at this elevation is almost entirely green, a few plants 

 only,, especially if growing in open clefts or glades in the forest, having 

 more or less reddish young leaves. Yet it is just here where a power 

 of stimulating transpiration is apparently most needed; for at this 

 elevation the air is, during the greater part of the time, at or near 

 saturation-point. On the other hand if the red pigment acts as a pro- 

 tection against sunlight, it is easy to understand why here, where the 

 sun rarely shines for more than a few hours daily and then generally 

 through a haze of clouds, the protective red pigment should almost 

 entirely disappear; for it is just the more refrangible photochemical 

 rays which the air saturated with water-vapour absorbs in greatest 

 amount." 



And again, " In Java at the commencement of the wet S.W. monsoon 

 and in Ceylon at the rainy commencement of both monsoons, the 

 vegetation acquires a more marked reddish tinge than the dry periods 

 between the monsoons. This is, however, simply due to the fact that 

 the young foliage, which in most tropical plants is more or less tinged 

 with red, is very much more abundantly formed at this period than 

 during the dry season. Even during the wet season in West Java, 

 there is almost always bright sunlight until mid-day, lasting often till 

 3 or 4 p.m., and occasionally all day; so that the young foliage which 

 the rain has caused to be produced in such abundance is exposed for 

 six hours on the average to very bright illumination, the sunlight from 

 9-12 being the brightest of the day. Hence the protective red coloura- 

 tion is perhaps quite as necessary during the wet season as during the 

 dry." 



The question as to the significance of the non-development of pig- 

 ment in the stomata in leaves with red epidermal cells is also considered 

 by Ewart. Stahl's view is that the stomata by this means transpire 

 less, and so are able to keep open longer for purposes of transpiration 

 and photosynthesis. Ewart, on the contrary, regards the absence of 

 anthocyanin as being due to the fact that the stomata are organs which 

 react to light, and it is important that they should be exposed to the 

 same intensity of light as that falling on the rest of the leaf even at the 

 risk of injury. 



Again, Stahl, as we mentioned previously, looks upon the develop- 

 ment of anthocyanin in stigmas of anemophilous plants as an adaptation 

 for increasing the temperature and aiding the growth of the pollen-grain. 

 Ewart, however, notes that it has been shown that the pollen-tube 



