1893.] THE MICROSCOPE. 57 



parent membrane, is of a corky character, and nearly impervious 

 to air and moisture. This is very well developed here, as in 

 many other evergreen leaves, to which it renders an important 

 service in protection from atmospheric conditions. It does not 

 take the stain here. 



Below the epidermis are two tiers, more or less, of nucleated 

 chlorophyll-bearing, columnar cells, some four or five diameters 

 long, rather closelv packed together in the '• palisade " style at 

 right angles to the plane of the surface. This dense, sub-epider- 

 mal tissue, which is well seen only in thin tip at the end of the 

 section, constitutes nearly the upper half of the leaf's thickness. 

 By its compactness it gives the firm texture and the dark green 

 color to the upper side of the living leaf, and enables it to main- 

 tain an active state as an evergreen during long periods of heat 

 and dryness. 



The lower half or more of the blade is a loosely arranged, spongy, 

 parenchyma, with much larger, thin-walled cells of irregular 

 forms and sizes, with rounded outlines little flattened by crowd- 

 ing, and easily permeated by air on account of the numerous 

 intercellular spaces thus remaining. Near the bottom the cells 

 are smaller and more compact, and therefore polygonal, form- 

 ing a moderately dense hypodermal tissue, and covered below by 

 an epidermis and cuticle, which are not so well developed as those 

 of the upper surface. * * * 



The fibro-vascular bundles which constitute the framework 

 of the leaf are, where they happen to be cut transversely, finely 

 displayed by the yellowish-green staining ; and with their abun- 

 dance of large ducts and of very thick-walled fibres they are seen 

 to be remarkably adapted to the two objects of the structure — the 

 firm support of the blade, and the rapid transmission of sap. Sev- 

 eral dashes of green staining, at many points along the centre 

 of the thickness of the blade, indicate spreading fibro-vascular 

 bundles of unequal degrees of perfection, from well-formed bun- 

 dles to mere hints of the same ; and at various degrees of obliquity, 

 from longitudinal to nearly transverse. The longitudinal, which 

 should be most instructive, are badly handicapped by being 

 buried in such an excessive thickness of section ; the oblique are 

 showy, but so confusing that it is difficult to make out anything 

 accurately about them — a fact which is common to oblique sec- 

 tions generally, and which has caused them, though showy and 

 formerly popular, to fall into disuse. 



One of the most attractive and profitable experiences for a be- 

 ginner in microscopy is to cut sections of various fresh leaves, 

 and examine them carefully in water under a cover-glass, if not 

 supplied w T ith many permanent mounts, looking for the various 

 features above described, and noting how they vary in different 

 plants. 



