RESPIRATION AND FERMENTATION 123 



to some 5-10 mm. radicle length, for thus their progress may better be watched, 

 their growth is more active, and bad ones may be excluded. The best tem- 

 perature for growth is about 28 for these seeds, though the process here 

 under study is more active at a higher temperature. A good proportion of 

 seeds to chamber capacity is about one oat or barley grain to each 10 cc. 

 capacity, though more seeds will give quicker results. It is of some advan- 

 tage, though for this purely qualitative experiment not necessary, to start 

 the experiment with the mercury some distance up the tube, for thus an 

 expansion, as well as a contraction, of the contained gas may be shown. This 

 may be effected by tipping the tube at the surface of the mercury, or, better, 

 by sucking through an inserted fine rubber tube. 



Respiroscopes. These may be of any form offering a gas-tight cham- 

 ber for the working tissues in continuity with a tube in which a visible gas 

 test may be applied. A good form is described by Detmer, 261, and a very 

 convenient form is the normal respirometer later described. A number of 

 adapted forms, all made up from common articles of the laboratory, are 

 shown by the accompanying figure (Fig. 30). In all cases the open end 



A BCD E F 



Fig. 30. — Various forms of respiroscopes; Xi- 

 Explanation in text. 



stands in a small dish of mercury (or other chosen reagent), and moisture 

 is supplied the seeds by wet wool or sphagnum, or by a few added drops of 

 water. The form A, made from an ordinary U tube (as described in Eotan- 



