,300 PHYSIOLOGY. BOOK II. 



enabling it to "preserve the unalterability" to which its pre- 

 servation is owing. This superfluous carbon renders it 

 scarcely soluble in water. To enable the parts to be suffi- 

 ciently moistened, it is consequently necessary that the seed 

 shovild be decarbonized by the oxygen of the air. This ex- 

 plains why Peas scarcely ripe will germinate much more 

 rapidly than those which are fully matured ; the former con- 

 tain more pure water and less carbon. In fact, the effect of the 

 abstraction by oxygen of the fixed carbon is to bring back the 

 seed to the state in which it was before it was provided with the 

 means of remaining unchanged in a torpid state. The sweet 

 taste of germinating barley is, in reality, what the seeds pos- 

 sessed befoi'e they were finally hardened. The destruction of 

 the oxygen of the air by the carbon of the seed produces a 

 sensible heat in germination, just as a similar cause produces 

 a similar effect in flowers when the foecula of their disk is 

 converted into sugar (see p. 276.). Hence the heat of masses 

 of Barley which are made to germinate in darkness in order 

 to become malt. And it can scarcely be doubted, that the 

 change of the starch of that grain into sugar is chemically 

 owing to the abstraction of a proportion of its carbon and the 

 addition of some other proportion of oxygen. 



In the opinion of some persons, oxygen also acts as a stimu- 

 lant of the vital actions of the embryo. Humboldt remarked 

 that seeds plunged in chlorine, and taken out before the 

 radicle appears externally, germinate more rapidly than 

 ordinary; Cress, for instance, may thus be made to germinate 

 in 6 hours instead of 24 or 30. He even succeeded, by this 

 process, in bringing about germination in old seeds which ap- 

 peared destitute of the power. These experiments have not, 

 however, succeeded in all hands : in many cases it is possible 

 that the success that is said to have attended them has been 

 imaginary ; and, as the theory upon which the action of chlo- 

 rine was explained is now abandoned, one cannot avoid en- 

 tertainino; doubts as to the accuracv of the alleged facts. 



Heat it is in which the stimulus necessary to call the 

 vitality of seeds into action seems really to reside. No seed can 

 germinate at a temperature so low as that of freezing ; and 

 each seems to have some one temperature more proper for it 



