84 PHYSIOLOGY OF THE LEAF- 



others threw them back upon their stems, and exhibited a va- 

 riety of appearances. This phenomenon has been attributed 

 to the absence of light. A curious experiment was made by 

 a botanist, who placed the sensitive plant in a dark cave, at 

 midnight, and then lighted up the cave with lamps ; the leaves 

 which were before folded up, suddenly expanded, and when on 

 the following day the lights were extinguished, the leaves again 

 closed. 



The period at which the leaves fall off is termed the DefoU- 

 ation* of the plant ; about the middle of autumn, the leaves of all 

 annual, and of many perennial plants, gradually lose their vi- 

 gour, change their colour, and at length fall from their stems. 



The " fall of the leaf" may be referred tb two causes; the 

 death of the leaf, and the vital action of the parts to which it is 

 attached. If a whole tree is killed by lightning, or any sudden 

 cause, the leaves will adhere to the dead branches, because the 

 latter have not the energy to cast them off. The richness and 

 variety of colouring exhibited about the end of autumn, by our 

 groves and forests, is splendid beyond the power of the painter 

 to imitate. Yellow, red, and brown, are the most common 

 colours of the dying leaf; but these colours vary from the 

 brightest scarlet, and the deepest crimson, intermixed with every 

 shade of yellow, from the deep orange, to the pale straw 

 colour. 



Although we have said considerable upon leaves, yet, we have 

 merely touched upon the most important circumstances with re- 

 spect to them. You will, perhaps, be induced to pay piore at- 

 tention than formerly to them, in their different stages ; from 

 their situation in the bud, to their full growth and perfection ; 

 and will feel a new interest in their change of colour, when you 

 understand something of the philosophy of this change ; even 

 the dry skeletons of leaves, which the blasts of autumn strew 

 around us, may not only afford a direct moral lesson, but, indu- 

 cing you to examine their structure, lead you to admire and 

 adore the power which formed them. 



Appendages to Plants. 



Plants have a set of organs, the uses of which are less appa- 

 rent than those we have been considering ; but we should not 

 infer, because the design for which they have been formed is in 

 some measure concealed from us, that they were made for no 

 purpose, or exist by mere accident ; let us rather with humility, 



* From de, signifying to deprive of, and/oZtum, leaf. 



Defoliation Fall of the leaf Concluding remark Reflections upon the use 

 of certain organs. 



