take place in plants through the membranes covering their cells and vessels, which may be compared to the bladder in the figure. By means of this force, in part, as well as capillary attraction, the movement of the sap takes place. This, however, will not account for it entirely, and we must look to other causes besides those of a physical nature in determining the movements of fluids in living bodies. We shall find that the process of exhalation, or giving out of fluid from the leaves, materially assists these agencies; and in the case of laticiferous vessels, the conspicuous movements of the sap in them appear to be influenced by some vital powers, not yet determined. In fig. 85, is given a drawing of these vessels in the celandine, with arrows indicating the course of the fluids. The movement requires a good microscope in order that it may be seen, and also demands careful management so as to avoid all source of fallacy. The peculiar sheath which covers the leaves of the India rubber fig in its young state, is one of the best objects for showing this circulation, which ought to be looked for when the plant is growing, and in circumstances in which no injury is inflicted.

85. Various are the uses to which the woody stems of trees are applied. The heartwood of exogens is more durable than the outer or sapwood, and is less liable to attacks from dry-rot, which is caused by the growth of a peculiar kind

of mould.

The outer bark often becomes very thick, and in the cork oak (fig. 19, p. 36), it supplies the important substance called cork. inner bark is fibrous, and is used to furnish ropes

The

and mats. What are called Russian mats are procured from the inner bark, the bast, of the lime tree. The inner bark of the lace-bark tree exhibits beautiful meshes like lace. Hemp and flax

Fig. 85.-Portion of the leaf of Celandine, showing the laticiferous vessels in which movements of fluids take place, as indicated by the

arrows.

are the produce of the part of the plants which corresponds to the bark. A kind of hemp in India is procured from the inner bark of a species of Hibiscus. Many of the nettle tribe also yield useful fibres from the bark. The grass tree of China (Boehmeria nivea), which yields fibres used in manufacture, belongs to this tribe. The inner bark of trees is also used in some countries for manuscripts, and hence the name of liber or book applied to it.

VI. ON THE NATURE OF BRANCHES.

86. These are produced in the form of buds, which are connected with the centre of the woody stem. They occur especially in exogens, and they have the same structure as the stem from which they proceed. Branch-buds are arranged on the stem in a regular manner, and follow the same law of spiral symmetry as we shall see to be the case with the leaves. But, owing to various causes, it is rare to find all the buds properly developed. Many lie dormant and do not make their appearance as branches unless some injury has been done to the plant; others are altered into thorns; others, after increasing to a certain extent, die and leave knots in the stem. That thorns are, in reality, undeveloped branches, is shown by the fact that they are connected with the centre of the stem, that they bear leaves in certain circumstances, and

that under cultivation they often become true branches. Many plants are thorny in their wild state, which are not so under cultivation, owing to this transformation. Thorns, as of the Hawthorn, differ totally from prickles, such as occur in the rose. The latter are merely connected with the surface of the plant, and are considered as an altered condition of the hairs, which become hardened in their structure.

87. In the curse which God pronounced on the soil when man fell, he said, "Cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life. Thorns, also, and thistles shall it bring forth to thee." (Gen. iii. 17, 18). May we not see, in the production of injurious thorns, an arrestment by the fiat of the Almighty in the formation of branches, and thus a blight passed on this part of creation, a standing memorial of the effects of sin on what was declared at first to be very good? The same remark may be made in regard to prickles, which are well seen in the briar and bramble, and which may be considered as an alteration in the development of hairs, a change on them which is associated with injury to man. We often find thorns, briars, and brambles alluded to in the Sacred Writings as indications of the wrath of God against a backsliding and rebellious people. In Heb. vi. 8, St Paul says, "That which beareth thorns and briars is rejected, and is nigh

unto cursing; whose end is to be burned." In proclaiming the judgments of the Lord, Isaiah says, "There shall come up briars and thorns."(v. 6.) "All the land shall become briars and thorns."—(vii. 24.) "Thorns shall come up in her palaces, nettles and brambles in the fortresses thereof."—(xxxiv. 13.) So also Hosea says, "Thorns shall be in their tabernacles” (ix. 6), and “The thorn and the thistle shall come up on their altars." -(x. 8.)

88. Travellers in Palestine have particularly remarked the abundance of prickly and thorny plants in the land. Mr Dautrey, in his work entitled The Bible in Palestine, states, "That the plain near Tiberias is in many places a complete wilderness of thorns and thistles. They render some of the hills impassable, and entangle the foot of the traveller on spots formerly rich in culture." In many parts of Syria, cactuses form impenetrable barriers on account of their prickles. In the narrative of the Church of Scotland Deputation to Palestine, it is stated:-" Dr Keith, observing one of the adjoining hills to be very verdant and not very steep, set out for the purpose of climbing it. After a short absence, however, he returned to tell us that he had failed in his attempt. He found the surface overgrown with strong briars and thorns, through which he tried to make his way, but without success.' How complete the