PROCURING OBJECTS. 69 



glass, having another inverted over it, and then the lower one 

 heated over the flame of a spirit-lamp, the salt will be sub- 

 limed. Placed on the stage of a microscope, with a power 

 of 30 diameters adjusted to focus at the inner surface of the 

 upper glass, minute crystals will be seen to form of a bright 

 yellow color, which, as they cool, return to the original red. 



VEGETABLE TISSUES. 



Vegetable Tissues are prepared by tearing, making thin sec- 

 tions, maceration in water, dissection, or are examined in their 

 natural state. 



The spiral, dotted, and reticular vessels of plants require 

 generally to be dissected out, which is to be done under a 

 shallow magnifier. A single lens of one inch focus will an- 

 swer very well for this purpose. Having procured a piece of 

 asparagus, or the petiole of the garden rhubarb, &c., cut out a 

 piece about an inch long, split it open with a sharp knife or 

 scalpel, examine it under the magnifier, and separate with a 

 needle-point any of the vessels you require from the surround- 

 ing cellular tissue. This process is facilitated by dropping a 

 little water on the specimen. To prevent it moving, the speci- 

 men may be fixed with beeswax during the dissection. Ves- 

 sels, ducts, and cellular tissue, when prepared, should be kept 

 in spirits of wine until mounted. 



Fig. 23 represents the tissues in a longitudinal section of 

 Italian Reed j a, are cells of the pith ; b, annular ducts ; c, 

 spiral duct ; d y dotted duct ; e, woody fibre ; /, cells of the 

 integument. 



Cuticles. The external covering of plants, or cuticle, con- 

 sists of a thin membrane, adherent to the cellular tissue be- 

 neath it. Under the microscope it appears traversed by lines 



