LIMITING FACTORS TO GROWTH MEASUREMENTS. 337 



hours of the night or to part of the night. This difference 

 between the two plants seems to receive an explanation when we 

 contrast their general organization and habit of growth. In 

 the case of Agave each growing shoot is on a separate plant 

 and completely independent of every other. All the supply 

 of moisture obtained, whether from the soil by the roots or 

 from stores in the leaves, is available for the one growing shoot. 

 Again, with such thick and fleshy leaves with thick cuticle 

 the loss of water from the leaves must be quite small even in 

 conditions of intense light and low humidity. It does not 

 seem surprising, therefore, that the supply of water to the 

 growing axis should be sufficient even in the hotter and drier 

 parts of the day. 



The case of Dendrocalamus, on the other hand, is quite 

 different. The culms grow in clumps from a complicated 

 network of underground rhizomes. The supply of water 

 available is drawn upon, not only by the growing culm , but 

 also by a number of adult culms on the same rhizome. Each 

 adult culm has a large area of thin leaves spread out to the 

 atmosphere. Changes of light, intensity and of humidity of 

 atmosphere must have a great effect upon such a system 

 of thin well-spread leaves, and the amount of water transpired 

 by the adult culms no doubt varies very largely with changes 

 in these conditions. Thus the amount available for the grow- 

 ing culms, which have themselves no leaf -system which would 

 draw up their own supply of water, must be largely a matter 

 of the amount left over when the adult culms have been satis- 

 fied. 



Thus we have two cases in which the actual rate of growth 

 of the shoots depends upon the same factors, but on each in 

 different degree according to the specific organization and 

 habit of the plant. 



4. OTHER CASES. 



We now turn to cases of the growth of plants of very different 

 character and habit. The gardens at Peradeniya offer several 

 9(8)06 (31) 



