YALE AGRICULTURAL LECTURES. 35 



FOURTH DAY. FEB. 4, 1860. 



A change has been made in our programme. Instead of 

 the third lecture being at seven in the evening, it is transferred 

 to half past three in the afternoon, the usual hour for the second 

 lecture, which, by this arrangement, will be changed to quarter 

 past two o'clock, the two lectures following one after the other. 

 This plan is to accommodate persons who, living out of town, 

 wish to hear .all the three lectures, and return home before 

 evening. 



Professor JOHNSON gave a lecture last evening, on the "At 

 mospheric Food of Plants," reserving a consideration of their 

 inorganic food for this morning. The larger part of the sub 

 stance of plants is, as every intelligent farmer knows nowa 

 days, obtained from the air ; a fact fully proved in the simple 

 experiment of burning wood in our stoves. A log of wood so 

 large as to require two men to roll it on to the fire, burns away 

 so that, after a time, nothing remains but a shovelful of ashes, 

 so light that a child can carry it out. Where has the log gone 

 to, and where have the myriad million tons of trees, plants, 

 and animal bodies gone to, which, in past ages, grew upon the 

 earth ? They have each borrowed a little mineral matter from 

 the ground, and a vast quantity of gases from the atmosphere, 

 out of which all their roots, trunks, stems, leaves, and branches 

 have, with wonderful skill, been built. The animal feeding 

 upon the vegetable it, too, has built up its structure from these 

 same original elements. In both plant and animal the season of 

 life was followed by a time of death, and the organized body 

 resolved into the gases and minerals, the use of which it had 

 borrowed for a brief season. Professor Johnson explained the 

 gradual progress of knowledge of atmospheric constituents, 

 until one day none of its ingredients remained unknown ; and by 

 means of the few well-known experiments he demonstrated the 

 nature and properties of each. When the source of the car 

 bon of plants was still a matter of dispute, Boussingault, the 



