THE LOWER FORMS OF LIFE. 15 



herbivorous animal takes the food thus manufactured, and then 

 others higher in the scale kill and feed upon the meat which it pro- 

 duces, and thus the great chain of animal existence is preserved. 



It would be an insult to the imagination and intellect of my readers 

 were I to dwell upon the beautiful and sublime thoughts which the 

 mere mention of this great chain of facts must create in their minds. 

 But in these pages I do not intend to get too much into what Mr. 

 Newman happily calls " the groove." I wish rather to read with 

 them the book of nature as seen in its inner aspect, and to create, if 

 I can, that real love of the grand facts it presents to us which is felt 

 by all who prefer indulgence in the pleasures of intellect to those of 

 sense. 



The first great function performed by leaves is to get rid of the 

 excess of water drawn in by the roots. This is done by exhalation 

 through the stomata, under the influence of light and warmth. 

 This exhalation is much larger than ordinary observers have any 

 idea of. A cabbage, for instance, is known in a warm day to exhale 

 as much fluid as its own weight. Some idea may be formed of the 

 quantity of fluid given off by the grass on a common lawn by 

 placing an inverted tumbler upon it in sunshine, and observing the 

 rapidity with which drops of water form on the glass inside. This 

 experiment is best performed, as it was done by Bishop Watson, after 

 several weeks ' dry weather. He calculated that a meadow, so cir- 

 cumstanced and cut, during hot sunshine exhaled 6400 quarts of 

 water in twenty four-hours. Dr. Carpenter has, however, noticed 

 that the bishop did not allow for the fact that all exhalation is 

 stopped during the night. But if we divide this by two, still 3200 

 quarts per acre during twelve hours is an enormous quantity, and 

 will give us some idea of the rapidity and importance of this 

 function of leaves. 



The excess of fluid being thus removed by exhalation, the in- 

 organic or mineral matters brought into the leaf by the roots are in 

 a fit condition to unite chemically with the organic matter taken in 

 by the stomata from the atmosphere. This function is termed, as in 

 our bodies, that of respiration, and just as our blood by breathing is 

 converted from venous into arterial, so is the crude sap changed by 

 the breathing of the plant into the nutritious fluid known as true 

 sap. During the process of human respiration, oxygen gas is appro- 

 priated and carbonic acid is given off ; during that of the plant, the 

 opposite, as we have seen before, is the case carbonic acid is taken 

 in and oxygen given off ; and thus it is that plants purify our 

 atmosphere. 



In addition to the respiratory functions, there is another going on 

 in leaves which has some analogy to that of our digestion. All the 



