METABOLIC PROCESSES IN THE PLANT. 259 



of the seedlings, especially in the hypocotyl, since the carbohy- 

 drates necessary for the regeneration of proteids could not be 

 produced. At the time when the plants deprived of Carbon 

 dioxide contain an abundance of asparagin, those growing under 

 normal conditions, and constantly increasing in vigour, no longer 

 contain asparagin, or at most only small quantities of it. 8 



If seedlings of Lupinus are grown in the dark, they die after 

 some time, and are here again rich in asparagin, since under 

 these conditions the non-nitrogenous material necessary for the 

 regeneration of proteids is wanting. All this can be made out 

 by microchemical investigation (see 98) or by analysis (see 99). 



1 See Pfeffer, Pringsheim's Jahrbiicher, Bd. 8. 



2 See Pfeffer, Botan. Zeitung, 1874, p. 249. 



II. RESPIRATION. 

 101. General Experiments on Respiration. 



THI-: methods to be employed in accurate researches on respiration 

 will be discussed in the sections following. We are here at first 

 only concerned with demonstration experiments, which will afford 

 us a general view of the different forms of plant respiration. 



We procure two wide-mouthed glass cylinders. In one we put 

 good quantities of flowers or seedlings (wheat, peas, beans), and 

 then close both of them with glass stoppers or corks. After a few 

 hours we introduce into each cylinder a burning taper supported 

 by a wire. The flame is extinguished in the cylinder provided 

 with plant material ; in the other it goes on burning. The respir- 

 ing plants have used up the Oxygen of the air within the cylinder, 

 and produced Carbon dioxide, which is unable to support combus- 

 tion. 



This simple lecture experiment we associate with another, which 

 directly proves the production of Carbon dioxide as a result of 

 normal respiration. We put together the apparatus represented 

 in Fig. 93. The bottle, of about 10 litres capacity, and filled with 

 water, serves as an aspirator. It is fitted with a two-holed cork, 

 through one hole of which passes the tube G. This is connected 

 up with the tube It, which is provided with a glass stop-cock. 

 Before the experiment begins, the tubes G and E are filled with 

 water. The tube G' is in connection with a, b, c, and d. The 



