;~n SMITH : VH'UC \TION OF THE THEORY OF 



some difference, even if small, between the different parts 

 i if the year as far as their suitability to growth is concerned. 



A plant therefore with large stores of reserve is able, so to 

 speak, to choose the most favourable time of the year for its 

 growth and to store materials during the remainder. This 

 resting period, though not so favourable for growth, is favour- 

 able for assimilation and storage, and so. on the whole, the 

 plant may gain by this division of function. 



In conclusion, I wish to express my thanks to Dr. J. C. Willis 

 for constant help and suggestions throughout the course of the 

 research and to Mr. F. F. Blackman, upon whose work the 

 whole paper is based and whose paper on Optima and limiting 

 factors first suggested this work to me. I am also greatly 

 indebted to Mr. H. M. Leake, Government Botanist. Saharan- 

 pur. who was kind enough to take for me some measurements 

 of Agave Sisalana, to Lieut. -Col. Prain and Mr. J. R. Drum- 

 mond of Kew who forwarded valuable information on the 

 species and distribution of Agave and Furor aea, and to Mr. 

 Francis Darwin who kindly supplied me with information 

 regarding transpiration and stomata. I have been aided 

 throughout by the help of the staff of Peradeniya and am 

 especially grateful to Mr. H. F. Macmillan, Curator of the 

 Botanic Gardens at Peradeniya, and to Mr. J. K. Nock, Curator 

 of the Hakgala Gardens, for their help in carrying out the 

 MliM-rvations at these two places. Mr. W. T. Southorn, 

 Assistant Government Agent at Anuradhapura, kindly placed 

 the resources of the (late) Botanic Gardens there at my 

 disposal. 



SUMMARY. 

 1 . The object of the research was to test the theory of Limit - 

 mg Factors by application to growth measurements in Ceylon. 



L'. In the case of the inflorescence axis of Agave and 



I'um r.ia the growth was controlled by the temperature 



throughout. Observations of the interna] temperature of 



i /hi make it probable that the internal temperature 



tli«- true Limiting factor. 



