Comparative Physiology. 351 



collected there being needful in germination. Seeds germi- 

 nating naturally have been found to throw off acids and accu- 

 mulate alkalies; and seeds bottled in alkaline solutions have 

 been found to germinate more quickly than natural, while those 

 bottled in solutions of acids have been found to vegetate in a 

 retarded imperfect manner. It is not likely that the functions 

 in germination are confined wholly to the conversion of starch 

 into sugar ; though the most obvious change, it will require to 

 be followed up by the preparation of the latex, or life blood, of 

 the plant. Dumas says all the tissues of vegetables commence 

 being formed from an azotated matter called vegetable fibrine, 

 similar in its projoerties to the fibrine of the blood of animals ; 

 it is contained in the grey milky substance first deposited in 

 seeds ; and when seeds germinate we again find it in the coty- 

 ledons. The substances dejDosited as food are probably, there- 

 fore, at least in part, converted into their elements, from which 

 the latex containing fibrine, mucilage, &c., is formed. The fibrine, 

 the insoluble nitrogenised constituent of seeds, must be again ren- 

 dered soluble, new fibrine also formed, and the other substances 

 decomposed and recomjDosed into a state fit for assimilation. 

 The peculiar juices vary much in different plants ; it is difficult 

 to get them in a pure state, being generally mixed with the 

 ascending sap in the act of extracting. In the present state of 

 vegetable chemistry, Professor Thomson says, " an accurate 

 detail of their properties cannot be attempted ; the cambium, 

 however, Avhich, according to Mirbel, makes its appeai'ance in all 

 those parts of vegetables where new matter is being formed, is 

 entirely mucilaginous." Much chemical decomposition and re- 

 composition is probably required in forming the vital fluid for 

 assimilation. 



On the pressure of the atmosphere, he notices the effects of 

 violent and sudden changes on animals : " Though it cannot 

 be regarded as a vital stimulus, yet it has an important in- 

 fluence on the functions of life. The whale can dive in 

 the water to the depth of 100 fathoms, at which depth the pres- 

 sure is twenty times greater than at the surface, and where the 

 sword-fish and its other enemies are unable to follow ; the 

 condor, also, can dart from the highest peak of the Andes to 

 the brink of the sea, passing through a barometric pi'essure of 

 from 12 to 28 inches : but the greater number of aii*-breathing 

 animals are adapted to reside on the surface of the earth, sub- 

 jected to the usual pressure of the air. It is probable that 

 man, ]30ssessing as he does in so remarkable a degree the power 

 of adaptation to external circumstances, could supjoort life 

 under any degree of rarity of the atmosphere which will main- 

 tain tliat of other vertebrated animals ; but the rapid change 

 from the ordinary pressure to one much less in amount is 



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