220 



ZONES AND REGIONS [Pt. Ill, Sect. I 



The figures observed in reference to the growth of several plants of 

 Taeniophyllum, in their native habitats, are given in the following table, 

 which also includes data regarding the photic ration which is an im- 

 portant factor. 



GROWTH IN LENGTH OF ROOTS OF TAENIOPHYLLUM ZOLLINGERI 



(after Wiesner). 



Compared with the greatest diurnal increment of a bamboo-culm as 

 given by G. Kraus the greatest increment of Taeniophyllum is as 570 : 

 0-283 mm. or 2013 : [. Hence the culm of bamboo observed by Kraus 

 grew in round numbers 2,000 times more rapidly than the aerial roots of 

 Taeniophyllum Zollingeri. 



Transpiration. 



The great physiological importance of the heating of plants by insola- 

 tion and the part played in this matter by transpiration are very easily 

 observed, and have quite recently formed the subject of closer investigation. 

 The action of insolation is stronger when the air contains much water-vapour 

 than when it contains little, because dryness of the air causes the stomata 

 to close. The effect of insolation is consequently most strikingly observed 

 in moist districts. 



Every visitor to the botanic garden at Buitenzorg knows that many 

 plants, during the later hours of the generally sunny forenoon, usually 

 exhibit clear signs of incipient wilting ; this continues to increase rapidly 

 until the occurrence of the afternoon shower of rain, by which time many 

 leaves hang down quite in a drooping condition, although they are not 

 unprovided with protective contrivances against transpiration \ During 

 my visit to Buitenzorg in the midst of the rainy season, fourteen rainless 

 sultry days passed in succession, and the vegetation presented a parched 

 appearance such as would hardly have arisen in Europe after a period 

 three times that length ; the crops were endangered and the population 

 sought by appropriate weeping-ceremonies to invoke the favour of the 

 Rain-god. The air remained very moist throughout this dry period, and, 

 in a less sunny climate, the rich nightly formation of dew would not have 

 been so ineffective. 



1 See p. 18. 



