194 WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 



254. Respiratory Ratio in Peas and Beans. With a 



suitable respirometer ascertain the respiratory ratio (relation 

 between carbon dioxide released and oxygen absorbed) in the case 

 of Peas or Beans. In these and various other seeds the respiratory 

 ratio is considerably more than unity that is, much more carbon 

 dioxide is released than oxygen is absorbed, and such seeds can even 

 release carbon dioxide in the absence of an oxygen supply. 



255. Respiratory Ratio in Oily Seeds. Set up two similar 

 respirometers. Weigh out equal quantities of (A) starchy seeds 

 like Wheat or Oats, (B) oily seeds e.g. Linseed or Hemp ; after 

 soaking the seeds place them in the two vessels, set side by side for 

 comparison. When oily seeds are ripening (after fertilisation) the 

 supplies of sugar they receive are changed to oil, and in this 

 process more carbon dioxide is given off than oxygen is absorbed 

 about five times as much, for instance, in Castor Oil. 



When the seed germinates the oils are changed back into sugar, 

 and for some time the amount of carbon dioxide given out is 

 considerably less than that of the oxygen absorbed. In an experi- 



C*O 

 ment with Linseed, the ratio 2 for the first six days was found 



to be 0-3, 0-35, 0'4, 0'5, 0'6, 0'7. As the conversion of oils into 

 sugar continues, the ratio gradually approaches 1. Also, during 

 the first few days of germination, oily seeds show an increase in 

 dry weight explained by the fact that carbohydrates contain 

 more oxygen than oils do. 



256. Respiration of Succulents. Set up two respirometer 

 experiments ; in A use as material leaves of Sedum, Crassula, 

 Rochea, or fleshy shoots of Cacti, cut from the plant at the end of 

 a warm day the material may be chopped into pieces ; in B place 

 leaves of some non-fleshy plant, e.g. Sunflower. Keep the 

 apparatus in darkness overnight ; in the morning note that the 

 fleshy plants have absorbed oxygen without giving out as much 

 carbon dioxide, so that the air in the chamber diminishes in 

 volume. 



In fleshy plants organic acids are produced by respiration in 

 such quantities that the formation of carbon dioxide may be 

 stopped altogether for a time. The amount of acid in the leaves 

 increases at night; the. accumulation of these would injure the 

 plant if continued, but after a time the plant begins normal 

 respiration, giving off carbon dioxide, which in sunlight is at once 

 assimilated, oxygen being set free. Hence in the morning, when 

 assimilation begins, fleshy plants give out more oxygen than they 

 absorb carbon dioxide, and they will continue to give out oxygen 

 in air freed from carbon dioxide. 



Succulent plants reduce their rate of transpiration, on account 

 of their xerophytic habitat, by having few stomata and small air- 



