48 



" A simple Dynamometer" 



In reply to the above criticism by Professor Barnes the under- 

 signed would say that it was not his intention that anyone should 

 interpret the method described as a way to estimate the total 

 imbibition force in all directions : but it is hardly possible, of 

 course, to make an experiment absolutely safe against misunder- 

 standing. The apparatus described by MacDougal * is about 

 the only one which will adequately represent this force. In this 

 method enough seeds are used so that the total thrust of expan- 

 sion is delivered within the range of the manometer. With 

 proper precautions however the apparatus described as " a simple 

 dynamometer " may be made use of for a comparative study of 

 the force of imbibition in one — the vertical direction. The pre- 

 caution is a simple one, namely that the scale be not overloaded, 

 or in other words that the amount of material used be coordi- 

 nated with strength of the spring. In common with other 

 apparatus of this type the critical point at which overloading be- 

 gins can only be determined by empirical experimentation. 



The same objections as those brought forward by Professor 

 Barnes could also be made to Pfeffer's spring dynamometerf or 

 indeed to the common lever dynamometer if the same precaution 

 is neglected. The apparatus described by Detmer ± is in effect 

 much the same, and the results obtained by it could also be 

 rendered of small import if a two gram instead of a two hundred 

 gram weight were used on the platform. 



It should indeed have been stated that it was a "2 lb." letter 

 scale which was used. The weaker scales might serve for in- 

 dicating force exerted by the downward growth of certain roots ; 

 ones in other words which were adapted to the strength of the 

 spring within the scale. — Herbert M. Richards, Barnard 

 Colleg e. 



*Journ. N. Y. Bot. Gard. 2: 39. Mr. 1901. 



jDruck und Arbeitsleistung durch wachsende Pflanzen p. 18 et seq. Leipzig. 1893 



% Practical Plant Physiology (translation), 142. 



