724 



CHEMICAL PROCESSES IN THE PLANT. 



The apparatus described in my Handbook of Experimental Physiology, p. 271, may 

 be easily employed, with the necessary modifications, for the observation of the pro- 

 duction of carbon dioxide and the elevation of temperature of germinating seeds. The 

 following experiment is also adapted for the demonstration of these points in a lecture. 

 One-third of a glass cylinder of 2 litres capacity is filled with soaked peas or some 

 other seeds or with flowers in the act of unfolding {e.g. small flower-heads of Com- 

 positae, as Matricaria or Pyrethrum)^ and closed with a well-fitting glass stopper. If 

 the vessel is opened carefully after several hours, the air contained will be found to 

 extinguish a burning taper let down into it, as if it had been filled with carbon dioxide. 



In order to observe the development of heat also in small quantities of seeds and 

 even in single flowers of larger size, I use various forms of the apparatus represented 

 in Fig. 472. The flask/ contains a strong solution of potash or soda / which absorbs the 

 carbon dioxide set free from the plants. In the opening of the flask is placed a funnel r, 



containing a small filter-paper perforated with 

 a needle. The funnel is filled with soaked 

 seeds or with cut flower-buds in the act of 

 opening; and a bell-glass g is now placed 

 over it, through the tube of which a thermo- 

 meter graduated to tenths of degrees is let in 

 so that the bulb is surrounded on all sides by 

 the plants. A loose plug of cotton-wool ^v 

 closes the tube. In order to compare the 

 temperature, a similar apparatus is placed 

 close beside, in which the seeds or flowers as 

 the case may be are or are not replaced by 

 pieces of moist paper or green leaves. It 

 is convenient to place both apparatuses in a 

 large glass case in order still more completely 

 to shield them from slow changes of temper- 

 ature in the air of the room. As the isolation 

 is not complete, the access of fresh oxygen- 

 ated air to the plants is not hindered, and the 

 continuance of respiration is therefore not 

 prevented; the arrangement is on the other 

 hand sufficient to reduce to a minimum the 

 loss of heat by radiation and evaporation. 

 The thermometers of both apparatuses, pre- 

 viously compared, must be frequently read 

 off" in order to detect the variations of tem- 

 perature. If the bulbs are small enough, the 

 elevation of temperature in the funnel may 

 be observed even with single flowers. In order to reduce still further the amount of 

 evaporation and radiation, it is convenient, before the bell-glass g is placed over, to 

 cover the funnel with a perforated glass plate, the thermometer being inserted through 

 its perforation. 



* It is possible under favourable circumstances to observe by means of this contrivance 

 a rise of temperature of 1-5° G. with 100 or 200 peas, while the roots are developing; 

 the anthers of a flower of the Gourd caused a rise of about o"8° G. in a tolerably large 

 thermometer with the bulb of which they were in contact on only one side. A single 

 capitulunf of Onopordon Acanthium produced an elevation of 0*72° G. ; the stamens of a 

 single flower of Nymphcsa stellata one of about o-6° G. The temperature of a number of 

 flower-buds of Anthemis chrysoleuca heaped round the thermometer rose as they unfolded 

 about 1-6° G. 



It will be readily understood that flowers must not be used for these experiments as 



Fig. 472. — Apparatus for observing the rise of temperature 

 in flowers and germinating seeds. 



