the upper edge.--_Orr's Circle of the Sciences._ [Verse: "And when he saw a fig tree in the way, he came to it, and found nothing thereon, but leaves only, and said unto it, Let no fruit grow on thee henceforward for ever. And presently the tree withered away."--MATTHEW XXI.] 1274. _Why have trees with large trunks a great number of leafy branches?_ Because it is _by the leaves_ that the secretion is formed which supplies the _woody fibre_. The number of leaves on a tree, therefore, generally bears a relation to the size of its trunk, and the number of its branches. 1275. _Why have poplar-trees comparatively few branches and leaves?_ Because their trunks are comparatively _small_, although they grow to a great height. 1276. _Why had the mammoth-tree comparatively few leaves in relation to the immense size of its bark?_ Because the woody texture of this tree (_Wellingtonea gigantea_) is _exceedingly light and porous_. It is, in fact, lighter than cork, and, therefore, requires less leaf-produce in its formation. 1277. _Why have oak-trees an abundance of leaves?_ Because their wood is _so dense_ that they require a larger amount of the wood-forming secretion which is supplied by the leaves. 1278. _Why are the trunks of trees round?_ Because, generally speaking, the leaves are distributed upon branches around the trees in every direction. They consequently send down the wood-forming principle on all sides. When a trunk is unduly developed on one side, it may generally be traced to the unequal distribution of the branches. 1279. _What are exogenous stems?_ Exogenous stems are those that grow by the addition of wood _on their outer surface_, underneath the bark. 1280. _What are endogenous stems?_ Endogenous stems are those that _grow inwardly_, from the centre. Trees of this class, of which palms are the best example, are almost peculiar to tropical climates. 1281. _Why do endogenous stems chiefly abound in tropical climates?_ Because, probably, the excessive heat of those climates would interfere with the _formation of wood from the sap_ upon the outer surface. The vascular structure of endogenous stems lying more abundantly towards their centre, tends to _conserve the juices_ which in hot climates are so highly valued. Palm-wine is a delicious and cooling beverage, and is procured from various kinds of palms, but especially from the cocoa-nut palm. Even the fresh sap is very refreshing. The juice is procured by cutting the tree in the upper part, and attaching a vessel to the opening, to receive the sap. Its flow is increased by cutting off a slice of the wood daily. [Verse: "I have caused thee to multiply as the bud of the field, and thou hast increased and waxen great, and thou art come to excellent ornaments."--EZEKIEL XVI.] 1282. _Why have endogenous stems no bark?_