Growth Measurements 177 



recording of data, that the scientist shows his true 

 calibre. It does not seem amiss, therefore, to 

 emphasize the importance as well as the difficulty 

 of this phase of any experimental project. 



Summary 



The significance of any piece of scientific work 

 rests primarily on the ability to express results 

 in quantitative terms and the reliability of these 

 terms themselves. The measurement of cultures 

 and the interpretation and evaluation of such mea- 

 surements are, thus, matters of prime importance. 

 Plant tissue cultures may be measured by deter- 

 mining protein nitrogen, dry weight, respiration 

 intensity, area, volume, and doubtless other char- 

 acteristics. The first three methods require the 

 destruction of the tissue studied. With callus 

 cultures none of these methods is fully satisfac- 

 tory and a subjective criterion can scarcely be 

 avoided. With root cultures linear increment has 

 been found to be a satisfactory criterion of growth 

 which is easily and accurately obtained, yet does 

 not involve destruction of the tissue studied. 

 Measurement of the central axis alone, ignoring 

 all branches, is in error by about 5 to 8 per cent 

 as compared to dry weights. Linear measure- 

 ments can be made with a mean error of 6 to 8 per 

 cent, an accuracy comparable to that obtainable 



