400 LECTURE XXV. 



nature. Even De Saussure found that the respiration of flowers is more energetic 



than the green leaves of the same plant, weight and volume being equal. The 



respiration of leaves, however (in the dark), again transcends that of shoot-axes and 



fruits. To mention a few examples only ; he found that the flowers of Liliiim 



candidum consumed five times their volume of oxygen in twenty-four hours, while the 



leaves, on the other hand, only consumed 2-5 times their volume. In Passiflora 



serraiifoUa the relation of flowers to leaves was 18-5 to 5*25, and so on. Even the 



individual parts of flowers respire with different energy ; thus. De Saussure found as 



follows : — 



Cucurbita Melo-Pepo. 



Volume of oxygen consumed 

 In 10 hoiirs. compared with that of 



the organ = i . 



Male flowers 76 



Female flowers - • • 3'5 



Anthers (separated from their bases) . . . . ii-7 



Stigma (separated from ovary) . . . . . 47 



In general, with normal conditions of respiration and sufficient access of 

 oxygen, the volume of carbon dioxide exhaled is equal to that of the oxygen taken 

 in, as De Saussure had already found. The same investigator also showed, however, 

 as long ago as 1804, that in the germination of fatty seeds this equivalence of volume 

 no longer exists : the volume of exhaled carbon dioxide is in this case smaller than 

 the volume of oxygen taken up. A portion of the latter, in fact, is not used for 

 respiration in the narrower sense of the word, but for the formation of carbo-hydrates 

 at the expense of the fats present, remaining meanwhile as a constituent of the sugar 

 in the plant. 



It is clear that the carbon contained in the exhaled carbon dioxide can only 

 be derived from the substance of the plant itself, and that a diminution of the 

 carbon contents of the plant must thus be eff"ected by respiration. Now this carbon 

 exists in the plant in the form of carbo-hydrates, fats, and proteid substances. Thus 

 if a part of the carbon escapes from these chemical compounds in the form of 

 carbon dioxide, they must suffer a profound decomposition which we may in 

 general term combustion ; and according to Boussingault's investigations, no doubt 

 remains that in this combustion, as is to be expected, water also is formed from the 

 organic substance. The loss in organic substance by means of respiration may, 

 under certain circumstances (e.g. during advancing germination in the dark, when 

 no replacement by assimilation takes place), even go so far that more than half the 

 organic substance is destroyed by respiration. In other words, the organic substance 

 of a seedling grown in the dark until it is completely exhausted, at last weighs only 

 half as much as the organic substance of the seed employed for germination, or even 

 less, and there is no doubt whatever that matters are exactly the same in the shooting 

 of buds and in growth without assimilation generally. 



From the investigation of Boussingault, however, results further the highly 

 important fact that this combustion effected by respiration concerns only the non- 

 nitrogenous constituents of the assimilated substance ; and since the fats are con- 

 verted into carbo-hydrates in metabolism, one may say only these latter are burnt to 

 carbon dioxide and water in respiration. This conclusion is fully warranted by 



