THE LEAF AS A PHYSICAL STUDY. 143 



ness portion, so to speak, — and he who would grow liis crop well 

 must understand the relationship. 



Putting aside its phj'siological histor}-, and looking at it from a 

 commercial point of view, we see grand and ever-increasing tests 

 of its utility as supplying food or comfort to man. Beginning 

 with our simple garden vegetables whose leaves are edible, we 

 stray from one item to another with augmenting interest, for we 

 find that our subject includes those leaves in vast abundance whose 

 medicinal qualities restore our impaired functions, — tea, the solace 

 of old women, with the leaves of thirty-two different species used as 

 substitutes, and as many more tried and rejected ; and tobacco, that 

 vile weed so universallj' used to soothe the pett}' and perplexing 

 cares of man. Our little leaf stores up food in the form of grain, 

 and grain we know forms the chief food of man, besides enabling 

 him to get rich on " corners." ]t furnishes dyes soft and beau- 

 tiful, and offers the artist subjects for his easel. The decorator 

 copies it to beautify the interior of our homes ; the architect refers 

 to it as the first material used in constructing dwellings ; and Holy 

 Writ assures us that it was the first article used for clothing by the 

 first human pair in the earliest historic period. The geologist finds its 

 impressions and petrifactions deeply' buried within the ground, and 

 infers much of earth's history therefrom ; the botanist revels in its 

 unending beauties, and lends his aid to the naturalist in solving 

 the vexed problem of evolution ; but to the phj-siologist alone are 

 its gigantic labors in making this world habitable for man revealed. 



Discussion. 



"William C. Strong thought Dr. Bowen's paper exceedingly 

 interesting. It had been impossible for him to conceive of any 

 means for the production of such vast quantities of carbon as are 

 found in the form of coal, but the theory that plants formerly had 

 the power of absorbing more carbonic acid than they do now 

 might account for these deposits. The remarks of the essayist on 

 this point had suggested to him whether it would be possible to 

 produce in our plant houses an atmosphere with an excess of 

 carbonic acid gas, as in the primeval ages, and thereby to increase 

 the luxuriance of growth. The possibilities of vegetable growth, 

 as seen in the tropics and sometimes in greenhouses, are extraor- 

 dinar}'. A single e3'e-cutting of a grape vine has in one season 

 made a growth of thirty-six feet. 



