Since the publication of Blackman's paper several 

 investigations havc appcarcd, which havo taken his thcory 

 into account. Thus in 1906 a paper was publishcd by A. 

 M. Smith, cntitled: .,0n the apphcation of the thcory of 

 limiting factors to measurements and observations of 

 growth in Ceylon", in which Blackman's theory of 

 limiting factors was subjected to practical tests. 



Smith has found, that with the main axis of the 

 inflorescence of Agave and Furcraea the température al- 

 ways limits the rate of growth. In this case thorefore the 

 température was continually the limiting factor. With 

 Dendrocalamus — which he investigated at three différent 

 places in Ceylon having différent climates — température 

 and water-supply alternately came into play as limiting 

 factors of growth; the water-supply itself was dépendent 

 on the humidity of the air and the light. 



In summarising Smith thinks the theory of limiting 

 factors a fruitful means for the explanation of many 

 différent phenomèna of growth, and in one case only he 

 does not succeed in reconciling ail facts with this theory. 



The further investigations founded upon the ideas of 

 Blackman deal primarily with van 't Hoffs law and 

 the variability of the optimum. 



In 1907 Smith published a communication of a few 

 lines on the respiration of Hydrilla verticillata. The intcn- 

 sity of respiration rises hère froni 7° C. — 50° C. accor- 

 ding to van 't Hoffs law with a coefficient 2.2forevery 

 rise of 10° C. An optimum with a subséquent decrease 

 is absent hère. 



In 1908 Law-rence Balls published figures on the 

 growth of fungus hyphae from which he concluded that 

 between 15° C. and 30° C. the growth in this case follo- 

 wed van 't Hoffs law. Because thèse experiments were 

 carried out by a method not wholly free from objections. 



