ON SAP. 69 



matter does not obstruct the passage of the sap till towards 

 the spring, when the vigorous sap is directed towards the 

 buds, and the old leaves drop offas the young ones expand. 



The petioles of some leaves, such as the aspen and the 

 poplar, are flattened, and adhere less firmly to the stem ; 

 hence they tremble at every breath of wind, and fall off 

 more readily than those of a cylindrical form.* 



With regard to the most important functions of the 

 leaves, the chemical changes they operate upon the sap, 

 we must reserve them for our next interview, which I 

 propose to dedicate to the examination of the sap, and 

 the interesting part it performs in the vegetable system. 



CONVERSATION V. 



ON SAP. 



Mrs. B. Now that you have made acquaintance with 

 the root, the stem, and the leaves, we may proceed to trace 

 the sap in its ascent through these several organs, observe 

 the various transformations it undergoes in the leaves, 

 and, following it in its descent, examine the manner in 

 which it feeds and restores the several parts of the plant. 



* The magnitude of leaves varies almost as much as their forms. In 

 the mosses which abound in cold climates, they are extremely minute; 

 and the forest trees of the North are adorned with leaves which appear 

 diminutive, when compareoSor rather when contrasted with the foliage of 

 Equatorial plants. There we find the leaves of the Banana, perhaps the 

 same which were employed by our first parents, to supply the want of a 

 more artificial dress; they being in the opinion of many writers the " Fig 

 leaves " of sacred history. In Ceylon, a country alternately exposed, for 

 many months in succession, to the rays of a vertical sun, and the inclem- 

 encies of an unceasing storm, is found the singular Talipot, a single leaf 

 of which is sufficiently large to shelter twenty men from the vicissitudes 

 of the climate in which they dwell. This tree is venerated by those who 

 find beneath its branches ,so kind a shelter, and travellers consider it, as 

 the greatest blessing which Heaven has bestowed on the country. And 

 when we regard its subserviency to the wants of the human race, it is not 

 surprising that by the ancients, the wide spreading tree, decorated with 

 leaves and occasionally beautified with flowers, should have been held sa- 

 cred as the very temple of the Deities they worshipped. 



371. Why do not the leaves of evergreens wither till spring! 372, 

 What is said of the leaves of the aspen and the poplar 1 ? 374. 

 What is said of the leaves of the Banana? S75.And of the 

 leaves of the Talipot? 376. What is to be the subject of the fifth 

 Conversation 1 ? 



