7 8 LECTURE V. 



Spike of Typha latifolia. 



absorbed in 24 hours 



Pistillate and staminate flowers mixed ... 9'8 vols. O. 



Staminate flowers 15* 



Pistillate 6'2 



Zea Mais. 



absorbed in 24 hours 



Spike of staminate flowers 9-6 vols. O. 



Spike of pistillate flowers 5' 2 



From his observations it appears that the absorption of 

 oxygen is most active when the flower is fully open. 



As to the absorption of oxygen by roots, it appears, from 

 the researches of de Saussure and of Deherain and Vesque, 

 that if the roots are not supplied with this gas, the plant will 

 soon begin to shew signs of unhealthiness, and will ultimately 

 die. It must not be concluded from this, however, that the 

 root absorbs oxygen and supplies it to the rest of the plant : 

 this effect is to be attributed simply to the fact that, in the 

 absence of oxygen, the roots become incapable of performing 

 their proper absorbent functions. With regard to the quanti- 

 tative estimation of the oxygen absorbed, de Saussure found 

 that a root, detached from the rest of the plant and placed in 

 a closed receiver containing air, will absorb a quantity of 

 oxygen which never exceeds its own volume : if, however, 

 the root be still in connexion with the stem and leaves of 

 the plant and these be outside the receiver, the root will 

 absorb many times its volume of oxygen. It appears from 

 this that the carbon dioxide formed in the isolated root 

 cannot escape from it after equilibrium is set up between the 

 gases of the root and those of the receiver. 



The following figures are taken from Dehe'rain and Vesque's paper : 

 in their experiments the roots were still in connexion with the stem and 

 leaves which were outside the receiver. 



Composition of the air in the receiver after the root 

 had been in it for 24 hours. 



Total quantity of gas in the receiver, 135*2 c.c. 

 Oxygen, 2 2 '6. 

 Carbon dioxide, 2*0. 

 Nitrogen, iio - 6. 



An equal quantity of normal air contains 28*34 c.c. of oxygen, and a 

 trace of carbon dioxide. 



