LECTURES ON BOTANY. 



117 



adapted to the fiilfillment of the offices allot- 

 ted to them by Providence, as to force them- 

 selves upon the attention of man, though too 

 distantly connected with his immediate in- 

 terests to admit of his due appreciation of 

 their value. Under myriads of modifications, 

 which our space will not pemiit us to inves- 

 tigate, this tissue constitutes the whole sub- 

 stance of the lichens, sen-weeds, mosses, and 

 other allied and equally neglected families of 

 plants. However different ui appearance 

 such cells are from the little tubes with which 

 they are found associated in all the nobler 

 classes of vegetation, there seems at present 

 to be scarcely a possibility of question that 

 the latter ai-e not merely the results of their 

 super-development ; in other words, that tlie 

 tube, under whatever form it may exist, is 

 but an elongated cell, or the breaking of the 

 cavities of several into one. These, however, 

 are speculations that we may hereafter i-efer 

 to more particularly ; let us look previously 

 at the tubes themselves, and note what is 

 known or understood respecting their uses in 

 tlie economy of the growing plant, and fii'st 

 at those w^hich compose the principal sub- 

 stances of the wood, its harder and tougher 

 portion, called woody fibre. 



Fig. 2. 



WOODY FIBRE. 



If the diameter of the cells just described 

 IS so small that without asuisfance from the 

 microscope we are generally unable to dis- 

 tinguish their cavities, tliat of tlie woody 

 tubes is fref|ueiitly much le.«s, ami in sonic 

 plants not more tlian tiie five-th<jus:indth of 

 an inch. Fig. 2 represents a small fragment 



1261) 



of oak wood highly magnified, showing it to 

 consist of such tubes closely disposed upon 

 each other, so as to occupy the smallest pos- 

 sible space, and leave no openings Vjetween 

 them, the narrow, tapering or attenuated ex- 

 tremities of each generally lying between the 

 broader portions of those that lie around 

 them. These tubes extend in the fonn of 

 continuous bundles or layers from one ex- 

 tremity of the plant to the other, sending out 

 branches into the leaves and other subsidiary 

 organs, and giving strength to, and maintain- 

 ing communication between all its parts ; 

 they constitute the channels through which 

 the sap ascends and is distinbuted, a fact 

 readily ascertained by cutting uito the stem 

 or branch of a vine, birch, or any other tree 

 in the spring, when that fluid may be traced 

 as flowing irom the mutilated vessels of the 

 wood. The passage of the sap through tliis 

 medium, though certified by long observa- 

 tion and repeated experiment, would appear 

 to those who examined the vegetable texture 

 for the first time, or without a previous ac- 

 quaintance with the natural phenomena con- 

 ' nected with organization, as an inexplicable 

 mystery, no apertures being discernible un- 

 der the highest powers of the micros<;ope, 

 through which the cavities of the woody tubes 

 communicate with each other. The dis- 

 covery, however, by Mons. Duti'ochet, of the 

 penneability of vegetable and animal mem- 

 branes, or that they are capable of transmit- 

 ting fluids through their substance, although 

 destitute of any apparent passage of commu- 

 nication — a phenomenon to which he gave 

 the name of Endostnosis — has contiibuted 

 gi-eatly to the elucidation of this and other 

 physiological facts, that were as stumbling- 

 blocks to the philosoi^hy of our forefathers. 

 The demonsti-ation of this important fact is 

 easy, and within the reach of those even whose 

 means of scientific inquiry are the most lim- 

 ited, as uistanced in one of the earliest ex- 

 periments of Dutrochet himself: he filled the 

 swimming-bladder of a carp (any other small 

 bladder will answer the same purpose, and 

 any fluid heavier than water) with a thin so- 

 lution of gum, and, placing it in a glass of 

 water, observed that the bladder swelled out 

 and became heavier, in consequence of the 

 water being attracted through its substance 

 by the weightier fluid within : he reversed 

 the experiment by iilling the bladder with 

 water, and placing it in the mucilaginous eo- 

 lutioii, under which circumstances it lost 

 weight, by the water passing out instead of 

 in. It was afterward ascertained by immer- 

 ous experiments tliat plants placed in water 

 draw it up through the thin tissue of their 

 cells and woody tubes, and acquire a great 

 increase of weight, which they lose again, at 

 the will of the experimenter, by simply add- 

 ing to the water in which they stand some 

 soluble substance, sugar, for instance, that 

 renders it heavier than their contained juices. 

 The iin-ce ol' this attraction, and of coui-se the 

 facility with which the fluid passes, is veiy 



