166 LEAVES FROM THE BOOK OF NATURE. 



This water, with all the materials it may contain, is sucked 

 up by the delicate fibres at the end of roots ; thence it 

 rises, probably by capillary attraction, upwards, transuding 

 through the cells by apertures invisible to the highest 

 microscopic power, and filling cell after cell. Here it 

 mingles with the fluid which they already contain, pro- 

 duces new combinations, and is then called sap. Hence 

 these little cells, when searched with the microscope, are 

 found to be filled with an almost incredible variety of 

 good things. Some, it is true, contain apparently nothing 

 but a watery juice, but its virtues may yet be disco- 

 vered ; others are little vials filled with gum or sugar ; 

 in many plants they are found to hold just one drop of 

 oil, and in others sugar, or to inclose beautiful crystals 

 of every possible shape. Through these cells the sap as- 

 cends, until it reaches the main workshop of plants the 

 leaves. These bring it in contact with the air, which they 

 in their turn suck in by minute openings and exhale again, 

 after it has combined with parts of the ascended water. 

 It is this continued exhalation of the leaves, and absorp- 

 tion by the roots, which constitutes the circulation, the 

 Life of Plants. They produce a constant interchange be- 

 tween soil and air, and stand in direct proportion to each 

 other. For the sap rises with a rapidity corresponding 

 to the exhalation of the leaves. Hence, in winter, when 

 there are no leaves, there is no sap ascending. Hence, 

 also, in spring the earth sometimes opens sooner than the 

 leaves appear ; the sap ascends, finds no outlet, and gorges 

 the tree with fluid. Man comes to its aid, taps the drop- 

 sical plant, and draws from the maple its sugar and from 



