•204 LEAVES. ^ 



to be revived by diminishing their discharge, or increasing ; 



their absorption. The former is accompHshed by confining j 



the air around them, and the latter by sprinkling water over \ 



the leaves ; and when plants have recently been removed, j 



audi management is frequently required, ' 



Air is not less essential to the healthy existence of ani- j 



mals than of plants. One great use of leaves is to perform, ] 



in some measure, the same office for the support of vegeta- = 



ble life, that the lungs of animals do for the support of ani- , 



mal life. Light has a very powerful effect upon plants, and 1 



the green colour of leaves is so much owing to it, that plants j 



raised in darkness are of a sickly white Light acts bene- \ 



ficially upon the upper surface of leaves, and hurtfully upon ] 



the under side ; hence the former is always turned towards j 



the light, in whatever situation the plant may be placed. A ] 



great number of leaves follow the sun in its course, and a 4 



familiar instance of this is a clover-field. The leaves of some | 



plants, when the light is withdrawn, fold over each other, or ^ 



droop as if dying ; and this is called by Linnseus the sleep I 



of plants. Some leaves display an extraordinary sensibi- ; 



lity to the touch of any extraneous body, or to any sudden J 



concussion, as those of the sensitive plant. An impression < 



made, in the most gentle manner, upon one of its leaflets, is ] 



communicated in succession to all of them, evincing an ex- I 



quisite irritability. The moving plant of India exhibits such ' 

 powers as to excite the astonishment of every beholder. If 



its motion be impeded, no sooner does it regain its liberty j 



than its operations are renewed with increased activity, as if ' 



it were necessary to redeem the time which it had lost. Its | 



winged leaves seem to disdain to rest, and to exhibit a most  



astonishing example of industry. \ 



Questions. — 1. What are the two parts of the root of a plant ? 2. i 

 How are roots divided with regard to their duration ? 3. Give the ') 

 examples. 4. What is said of buds ? 5. How is it proved that leaves | 

 are organs of perspiration, and of absorption ? 6. What office do \ 

 leaves perform for plants ? 7. What is the effect of light upon plants, j 

 and leaves ? 8. What is said of the sensitive plant ? 9. Of the ; 

 moving plant of India ? 10. Describe tho several kinds of Roots, i 

 (see Appendix.) 11. What is said of the root of common herds grass ? 

 12. What are the seven kinds of trunks or stems .•* 13. What are the 

 several kinds of appendages to a plant .'' 14. What are the several 

 kinds of Inflorescence ? 



