LIMITING FACTORS TO GROWTH MEASUREMENTS. 371 



3. In the case of the culms of Dendrocalamus the following 

 explanation on the lines of the theory of Limiting Factors 

 seems to fit all the facts : — 



Two factors of the physical environment in turn limited the 

 rate of growth of the culms, (1) the temperature of the culm, 

 (2) the supply of water to the culm. The second factor being 

 intimately connected with the amount of water drawn off by 

 the transpiration of the adult culms on the same rhizome, 

 depends in its turn on 2 factors, (1) the humidity of the 

 atmosphere, (2) the intensity of the light. 



4. The supposition that a growing organ is not capable of 

 continuous growth, but must have intermittent periods of rest, 

 though in harmony with some of my results, is inadequate to 

 explain others. 



5. A comparison of the cases of Agave and Dendrocalamus 

 shows that the correspondence between the rate of growth and 

 one or other of the factors of the environment depends largely 

 on the organisation and habit of the plant. 



6. The cases of the runner shoots of Capparis and Stifftia 

 are explicable on the hypothesis that the supply of water is the 

 limiting factor by day and the temperature by night. No 

 decisive case of retarding light effect was obtained. 



7. The growth of the hanging roots of Vitis Lindeni is limited 

 in January by the temperature, in July by the water supply. 

 This case is at present not to be fully explained by our theory. 



8. Consideration of previous work shows some cases which 

 can be explained by our theory, others in which the data are 



insufficient for its application. 



9. A general application of the theory to cases of growth 



from reserve material shows that the effective factors of the 

 environment are — 



(1) Temperature. 



(2) Water Supply. 



(3) Light. 



(4) Atmospheric Pressure. 



(5) Velocity of Wind. 



