CAB BON OBTALNED FROM THE SOIL. 33 



on goes down, a change takes place : an exami- 

 «.>v.v.a will now show that it is carbonic acid which 

 passes off from the leaves, and oxygen that is being 

 absorbed. It is just the reverse of what goes on during 

 the day. 



a. This curious fact shows why it is that plants 

 grow so rapidly in the long days of sununer. The 

 nights are then comparatively a small portion of the 

 day, so that for by far the greater part of the twenty- 

 four hours the plant continues to absorb carbonic acid, 

 and to build itself up with the carbon thus obtained 



b. In Greenland and Karaschatka the summer is not 

 more than two or three montlis, but during that time 

 it is always daylight, the sun scarcely going below 

 the horizon at all. Certain plants are thus enabled 

 to grow so fast as to mature and ripen their seed, even 

 in that short summer. We see now this beautiful 

 provision of nature tends to equalize different climates. 

 If the nights of the short Greenland summers were 

 even so long as our shortest, their crops would never 

 ripen; butasth<\ ' ' n 

 get enough f<xxl ; • .^ 

 a large part of their lung winter. 



tlCnON IT. CAKBON ALSO OBTAINBD BT PLANTS PBQM 

 TRB 80IU 



We see that plants are able to obi.tin mm h » .irl>on 

 from the air, but it is found that a rnnsid. rabK- quan- 

 tit\ 'he soil also. This is all, in one lorin 



or An in through the roots. The rain 



water whuh falls upon the surface, and all of the 

 spring water found tnere alrea«i\ . < mitains Mirin- i :ir- 

 bonic acid dissolved. This v 

 carries with it a variety of muo><iii<<:^ m 

 which the plant seems to use or not as it um 

 among tboie is carbonic arid. This is proi>ar>iy tne 



