ea 



"be rtinovoil finiii tliccliumln'i' ;in(l nl'liTwards a currt'Dt ol' air I'rci' I'l-diii carlioii diox- 

 1(U' 1k' l\)ri't'(l slowly tliroiifj^h tlu' cliainhor. As the air knives the fhaiuher it j)asses 

 thr(tii!;h a long Petteiikofer Iiarvta tuhe, containing a solution of barium hydrate, 

 and then through a siiuiiar luiI siiialh r tube, also containing bariiiin hydrate. ( )nly 

 •one long and one short tube are used at a time. When the first period is ended 

 tlie current of air is diverted to the other pair of tubes l)y the turn of a stopcock, 

 and in the meantime the first pair of tulu's is emptied, relilied witii fresh solution 

 and placed in readiness to be used when the seconil period is ended, and so on. 

 The solution from the lubes is titrated, and by a simple calculation the amount 

 of carbon dioxide exhaled by the plantlets ascertained for each period. 



The ap{)aratus is a modification of the one used by Prof. Pfef^er > Unters. 

 Bot. Inst, zu Tubingen, I, ').'!7 ), which in turn was an adaptation of Prof. Pet- 

 tenkofer's apparatus for studying the rt'spiration of animals. 



'2. The Centkifugai- Ai'PAratis is to illustrate Knight's famous experi- 

 ment in geotropism. The essential part of the apparatus consists of a closed 

 chamber kept moist by dripping water, in which a 

 cork disk is made to revolve. On this disk are pinned 

 germination seeds. This disk is revolved rapidly 

 ( from one hundred to five hundred revolutions a min- 

 ute ) for some time, and the position assumed by the 

 growing roots and the stems oljserved. The moist 

 chamber and revolving disk may be set horizontally, 

 vertically or at any intermediate angle. The speed is 

 uind by moving a paper over a pencil point at the 

 J- \ I thur Centrifugal h.ucr end of the spindle for a defi-nite time. It may 



be run by any convenient power, as a small water motor, or an electric motor. 

 The apparatus is an invention of the writer. 



:'>. Thk Gas Chamher, for use on the stage of the microscope, consists of a 

 shallow brass chamber, three inches long by one and three-fourths broad, with 

 projecting metal tubes at either end. One side of the chamber is provided with a 

 ida^s window, and the opposite side has a circular opening, which is to be closed 



when in use with the cover 

 glass bearing the object 

 for the experiment. The 

 object to be examined is 

 placed in a drop of water 

 upon the center of the cover glass. The glass is then inverted over the opening 

 'oi the gas stage, the margin having first been smeared with vaseline in order to 



l-JKure 



