PROPERTIES OF LEAVES. 75 



awaken plants to action as shown by placing the sensitive plant in a 

 dark cave and illuminating it with lamp light ; when it will suddenly 

 unfold its leaves and again close them on withdrawing the light. The 

 irritability of leaves is a remarkable phenomenon, as observed in their 

 motions on presenting the hand or other substances to them. This is 

 particularly notable in the sensitive plant. These leaves seem to be 

 much agitated, as if afraid of injury under such circumstances. 



The perspiration of plants is more abundant than in animals, though 

 in neither do we see it passing off except in cold weather. A root 

 placed in a bottle of water will withdraw it all and give it off in an 

 insensible perspiration. Thus a sun flower will perspire in a warm 

 day 30 ounces, or, as is said, 17 times more than a man ; but in the 

 night time little or none. The stem of a vine cut off near the head, 

 and a bladder secured tightly around it, will in the sun soon send off 

 sap enough to swell and burst the bladder. Plants, however, absorb 

 moisture during the night by their roots and are increased in weight in 

 the morning. Those in the shade, or in damp places, hence absorb 

 more than they loose, and the result is to render their parts soft and 

 watery. 



The power of leaves in sucking up moisture is evidently very great ; 

 as, upon a lofty tree, they act upon the roots at 3,000 times the distance 

 of their length. Roots placed in a warmer situation than that of 

 branches, absorb liquids faster than the leaves consume them, and the 

 sap often bursts through the stem and eventually destroys the excita- 

 bility of the tissue. In reversed situations the leaves, not receiving 

 sufficient sap from the roots, will die, the fruit will fall off, or the flowers 

 be unable to set it. One of the leaves of a branch taken off, if kept 

 constantly wet, will supply another below it with moisture, even 

 though the communication be intercepted. The powers and properties 

 of leaves and other organs of plants, vary much, however, in their spe- 

 cific nature and in their phenomena. 



Buds. 



Buds are divided into leaf-buds, containing the nidiments of leaves 

 without flowers ; flower-buds, containing the rudiments of one or more 

 flowers, folded over each other in scales, and mixed-buds., containing 

 both leaves and flowers. These, closely examined or cut through, pre- 

 sent beautiful incipient forms in progress cf development. Some con- 

 sider the bulb and turion as a species of bud. Leaf-buds, in most res- 

 pects are like bulbs ; they are commonly oval and are composed of 

 tough scales closely fitted together and covered with a gummy resin, 

 with a moist and downy substance between the scales for the protec- 

 tion of the embryo from the cold; while the external scales are dry 

 and hard. The embryo is thus often protected for years, even in 



