48 PROCURING OBJECTS. 



young branch of the misletoe, and the pith of the rubus odoratus, 

 present all the varieties. 



Woody fibre is best observed in vertical sections, cut either paral- 

 lel or perpendicular to the medullary rays. It consists of a series of 

 cells, which differ in exogens and endogens, and therefore sections of 

 both are extremely interesting. What is called glandular woody fibre 

 is peculiar to resinous woods, as the pine, which offers a good example. 

 In this case the microscope has greatly assisted geology, by proving 

 from this glandular structure that the coalbeds have been principally 

 composed of ferns and pines. 



Vascular tissue presents the most varied and interesting subject 

 for microscopic examination ; it consists of membranous tubes, inter- 

 nally furnished with fibre. The elder and asparagus give excellent 

 specimens of this tissue. 



45. SECTIONS OF TREES AND PLANTS. There is much tact re- 

 quired in preparing good and perfect sections of woods and plants. 

 The specimens from which they are to be cut must be in a proper 

 condition; the section should be of a uniform thickness, and 

 the various tissues and vessels unbroken. Indeed, an instrument is 

 required for the purpose of cutting them properly. The following 

 is one which is at the same time convenient and efficacious. A 

 represents a solid table of brass, 

 about six inches long, four wide, 

 and a quarter of an inch deep, with 

 a guide or stay-piece, rising above 

 the general surface at the back 

 edge B. C is a hole through A, 

 fitted with a short cylindrical Fig. 31. 



socket, that extends below the under surface of A ; it is close at 

 the bottom, except that the screw passes through it. The head of this 

 screw is made by a toothed wheel E, containing ten teeth, while the 

 screw itself contains thirty threads to the inch. The use of this screw 

 is to move up or down a brass cylinder with a square hole in it ; the 

 top of this is seen at D. The wheel, E, is kept in its place by the 

 spring F. I I is a three-sided brass frame, which has a sharp razor- 

 blade across it at I. K is the wooden stand to the whole. When used, 



