592 



BOTANY. 



tension and completion. Water is the principal 

 medium in which the elementary food of plants is 

 conveyed to them, and for the reception of which 

 their organs are so admirably fitted. The head of the 

 plant waving in the air is, from the previous structure 

 of its exterior surface liable to much waste by evapo- 

 ration ; this induces absorption of water at every 

 inlet ; and as these inlets are chiefly in the soil, where 

 there is always some degree of moisture, the latter is 

 readily received or absorbed : and hence a current 

 upwards is generated, to supply every waste, and to 

 fill and distend every vessel. 



If the sap be drawn from the stem by boring 

 near the root, it is found but little better than pure 

 water ; but if withdrawn from the top of the stem, or 

 from the branches, it is found much richer in essen- 

 tial qualities. This is proof that the aqueous food of 

 the plant undergoes a material change in the vascular 

 frame of the vegetable ; not only by simple admix- 

 ture with the essential juices, but by assimilation 

 thereto, by the agency of the peculiar elaborating 

 apparatus incident to the plant. Hence we have 

 resins, gums, acids, &c. Moreover, the elaborating 

 powers of plants are so great, that chemists have 

 detected chemical bodies in their juices, of which no 

 trace could be found either in the earth or water in 

 which they had been nourished. 



The motion of the sap is visibly and principally 

 upwards, also laterally, and downward. It is diffu- 

 sible in all directions ; passing into, and through every 

 membrane where there is depletion. In this re- 

 spect it is exactly like the absorption of water by a 

 piece of sponge, or a knob of salt or sugar. In a high 

 temperature, the sap is thin and its motion is accele- 

 rated. As heat declines, it becomes clammy, and in 

 the cold of winter it is quite stagnant. At all times 

 when in motion, and in sufficient quantity, it flows 

 from wounds made through the bark ; and when 

 exposed to air either assumes the consistence of resin, 

 gum, thick serum, or acidulous water. The recently 

 formed layers of bark and wood, are the principal 

 channel for the conduction of the fluids. When the 

 first-formed parts of wood cease to act as channels, 

 the sap becomes in them concreted in the cells and 

 intercellular passages, giving solidity, a darker colour, 

 and weight to the timber. This is very visible in 

 pine timber, and easily proved by maceration in a 

 proper acid. By such trials on oak and lignum 

 vitae, both colour and ponderosity are lost, and the 

 fibrous frame only remains, as light and as fragile as 

 that of willow. The outer layers of bark of many 

 trees, also become, after a certain time, useless as sap 

 ducts; and being no longer living members of the 

 tree, retain those concreted qualities, which were 

 deposited in their vascular substance when the sap 

 used to traverse them : instance oak bark. 



The annual subsidence of the sap from the branched 

 head, down in a body to the roots in the autumn, is 

 a very old and generally received opinion ; but it has 

 never been clearly proved. There are several cir- 

 cumstances which appear to militate against such 

 doctrine, and which, when stated, will enable the 

 reader to judge how far such an idea is worthy 

 acceptation. 



The roots are never so destitute of sap, nor so 

 capacious as to admit such an additional surcharge. 

 The sap in the branches is not visibly diminished 

 by such subsidence. The spring motion of the sap 

 begins at the top of the tree, before it is at all liquefied 



at the bottom, which could not happen did the 

 returning tide flow from the root. If we consider 

 the motion of fluids in general, and in all ordinary 

 circumstances, we invariably observe that their mo- 

 tions are caused by fluidity, ponderosity, or tem- 

 perature ; if they flow from a place which is full, it 

 is because there is a vacant space to receive them : a 

 rarer fluid will give place to one that is heavier ; and 

 consequently the warmest parts of a fluid will rise 

 above those which are colder. But in all these cases 

 an outlet or vacuum must exist, or the removal of 

 some pre-occupying fluid must take place before any 

 motion can be generated. 



These are a few facts bearing on the question, and 

 which must be explained away before we can fully 

 understand how a general subsidence of the sap in 

 autumn can possibly take place. It has been already 

 observed, that vegetable membrane is permeable to 

 fluids in all directions, and that the whole body of 

 fluid sap in the autumn is of congenial quality, and 

 equally diffusible into the roots as well as into every 

 other part of the system ; still direct proof is wanting 

 to establish the truth of the opinion, that a principal 

 portion of the sap of the head descends to the roots 

 in winter. 



SYSTEMATIC BOTANY. 



Systematic botany has no very alluring aspect to a 

 beginner. The great number of titles of the classes 

 and orders, to say nothing of the generic and specific 

 names, is a bar to commencing the study of the 

 science. But when set about in earnest, the first 

 difficulties quickly vanish ; still much attention and 

 time is required before such a knowledge of it can be 

 acquired as to yield real pleasure to the student. 



Initiation into this, like that of all other sciences, is 

 laborious ; stepping over the threshold is a kind of 

 mental drudgery, and which is in fact the most irksome 

 part of the undertaking ; but when the student is 

 fairly within the pale, the different avenues into the 

 interior and more occult regions of the science are 

 opened up ; those thick clouds of difficulty which 

 timidity or indolence had formed, are soon dispersed, 

 and the student soon finds himself in an open expanse 

 in a new world, where he finds a thousand new 

 objects which he can name at first sight. When this 

 much is attained, the study becomes every day more 

 and more interesting ; every new plant is sought and 

 examined with avidity : research is no longer toil ; 

 on the contrary, such investigation becomes delight- 

 ful exercise, yielding positive pleasure ; while every 

 accession to the previous stock of knowledge is 

 attended by fresh gratification. 



The amateur botanist proceeding in this way soon 

 acquires a competent knowledge of this pleasing 

 science ; he gradually becomes cognisant of the 

 greater features, and gains such an insight into the 

 details as dispels every obscurity which he thought he 

 saw before him on his first entrance on the study. 

 And when this much is accomplished, he enjoys every 

 satisfaction that can arise from the knowledge of one 

 of the most interesting branches of natural history, 

 and which, moreover, is a necessary accomplishment 

 of every well-educated mind. 



To ladies particularly, and to the young of both 

 sexes, the study of botany is a most agreeable exer- 

 cise and amusement. Flowering plants always claim 

 the regard of the young, of refined minds ; and none 

 are more enthusiastic lovers of fine plants than the 



