APPENDIX II 677 
leathery leaves. Such leaves should be prepared by boiling in 
10 to 20 per cent. aqueous solution of either sodium or potassium 
hydroxide until the epidermis puckers up in the form of blisters 
when the epidermis can be lifted off by means of fine forceps or 
dissecting needles and floated on the slide. 
SECTIONING IN PARAFFINE OR CELLOIDIN. 
When it is necessary to study the micro- 
scopic structure of very delicate plant parts, 
superior results can generally be obtained by 
imbedding the material in paraffine or 
celloidin (see pp. 692 and 699), which is 
-subsequently hardened, and sectioned by 
means of a sliding or rotary microtome. 
Kinps oF SECTIONS . 
1. A transverse or cross-section is one made 
horizontally through the object, hence its 
plane lies at right angles to the long axis. 
2. A radial-longitudinal section is one 
which is made parallel to the long axis of the 
object in such a way that it lies in the plane 
of the radius. 
3. A tangential-longitudinal section is one 
made parallel to a plane tangent to the 
cylinder. This type of section is therefore Fg. 504.—Showing 
prepared by cutting parallel to the outer the planes in which sec- 
long surface tions are cut, A, trans- 
i ‘ . versely; B, longitudinal 
4. A surface section 1s one made by Glin’ CO  tencieadk: 
cutting or stripping off the outer protective nal tangentially. (After 
covering of the plant organ. Stevens.) 
MICROTOMES 
Microtomes are instruments employed to facilitate the cut- 
of organic tissues. The three most commonly 
hand, sliding and rotary microtones. 
ONE.—Lhis type is shown in Fig. 505. If the 
hard to bear the strain, it is placed directly 
end of the tube that is tightened by the 
ting of sections 
used types are the 
Hanp MicrotT 
object is sufficiently 
in a clamp of the upper 
