136 COMPOUND ORGANS OF PLANTS. 



ever dissimilar the petals of the corolla may appear to the 

 ordinary leaves on the stem of some plants, so that we may 

 feel disposed to regard them as separate organs, yet the 

 evidence afforded by these transition forms shows the intimate 

 connection subsisting between the petal, the sepal, and the 

 bract, and the common origin of the whole of them from the 

 ordinary stem-leaf, of which they are but modifications. 



Functions of the Floral Envelopes. — The calyx and corolla 

 are by far the most conspicuous and showy parts of the flower, 

 and are the parts of it which usually attract popular notice. 

 Yet their functions are entirely of a secondary and subordinate 

 character. The internodes between the several whorls of floral 

 leaves are not developed, in order that they may the more 

 readily act on each other. The calyx and corolla doubtless 

 foster and protect the two inner whorls of leaves, viz. : the 

 stamens and pistils, which are more immediately connected 

 with the process of reproduction than they are. 



AU must have noticed the folding up of the calyx and 

 corolla at sunset, or in wet weather. The function exercised 

 by the two outer whorls of the floral leaves is in this case 

 clearly protective, and the design of their close proximity to 

 the stamens is at once apparent ; that they may fold over the 

 stamens and pistils, and thus ward off the injurious effect of 

 the night dews and falling rain, which would act injuriously 

 on the pollen contained in the cells of the anther. Thus 

 safely and beautifully sheltered at every epoch of their 

 development, the stamens and pistils perform their respective 

 functions. 



The bracts and calyx, when of a green color, doubtless per- 

 form the same functions as the ordinary leaves of the stem ; 

 but it is otherwise with the petals of the corolla and with the 



