PREPARATION OF YEGETARLE TISSUES. 405 



Dissection. — The former process is the most easy, and yields a 

 large amount of information ; but still it cannot be considered 

 that the characters of any tissue have been properly determined 

 until it has been dissected-out. Sections of some of the hardest 

 Vegetable substances, such as 'Vegetable-Ivory,' the 'Stones' of 

 fruit, the ' Shell ' of the Cocoa-nut, &c. (§ 290), can scarcely be 

 obtained except by slicing and grinding (§ 138) ; and these may 

 be mounted either in Canada Balsam or in Glycerine Jelly. In 

 cases, however, in which the tissues are of only moderate firm- 

 ness, the section may be most readily and effectually made with 

 the 'Section-Instrument ' (§ 137) ; and there are few parts of the 

 Vegetable fabric which may not be advantageously examined by 

 this means, any very soft or thin portions being placed in it 

 between two pieces of cork. In certain cases, however, in which 

 even this compression would be injurious, the sections must be 

 made. with a sharp knife, the substance being laid upon a slip of 

 glass. — In dissecting the Vegetable Tissues scarcely any other in- 

 strument will be found really necessary than a pair of needles (in 

 handles), one of them ground to a cutting edge. The adhesion be- 

 tween the component cells, fibres, &c. , is often sufficiently weakened 

 by a few hours' maceration to allow of their readily coming apart, 

 when they are torn-asunder by the needle-points beneath the 

 simple lens of a Dissecting-microscope. But if this should not 

 prove to be the case, it is desirable to employ some other method 

 for the sake of facilitating their isolation. None is so effectual as 

 the boiling of a thin slice of the substance under examination, 

 either in dilute nitric acid, or in a mixture of nitric acid and 

 chlorate of potass. This last method (which was devised by 

 Schultz) is the most rapid and effectual, requiring only a few 

 minutes for its performance ; but as oxygen is liberated with such 

 freedom as to give an almost explosive character to the mixture, it 

 should be put in practice with extreme caution. After being thus 

 treated, the tissue should be boiled in Alcohol, and then in "Water ; 

 and it will then be found very easy to tear-apart the individual 

 Cells, Ducts, &c, of which it may be composed. These may be 

 preserved by mounting in weak Spirit. 



298. Structure of the Stem and Root. — It is in the Stems and 

 Roots of Plants that we find the greatest variety of tissues in com- 

 bination, and the most regular plans of structure ; and sections of 

 these viewed under a low magnifying power are objects of peculiar 

 beauty, independently of the scientific information which they 

 afford. The Axis (under which term is included the Stem with its 

 branches, and the Boot with its ramifications) always has for the 

 basis of its structure a dense Cellular Parenchyma ; though this, 

 in the advanced stage of development, may constitute but a small 

 proportion of it. In the midst of the Parenchyma we generally 

 find Fibro- Vascular bundles ; that is, fasciculi of Woody-Fibre, with 

 Ducts of various kinds, and (very commonly) Spiral Vessels. It is 



