34 THE TISSUES OF PLANTS 
somewhat thicker, with less tapering ends and frequently 
with less thickened walls which are more strongly ligni- 
fied than those of bast fibers. 
Laboratory Studies. (a) Break the shell of a hickory nut, 
almond, coconut, walnut, peach-stone, etc., and after smooth- 
ing the broken surface, cut off a thin shaving, using a pocket 
knife or scalpel held at rather an oblique angle. Mount in 
water and a little potassium hydrate. The very small cell 
cavities show connecting pits or canals radiating from them to 
the original cell wall where they meet similar canals from the 
centers of adjoining cells, being separated only by the thickness 
of the original wall. Concentric markings are visible in the 
cell walls in some cases. 
(6) Determine whether the walls in sclerenchyma are made 
of cellulose or are lignified, by testing one section with a 5 per 
cent. aqueous phloroglucin solution followed by hydrochloric acid 
which gives a red color for lignified walls, and another section 
with iodine solution followed by somewhat diluted sulphuric 
acid which gives a blue color for cellulose walls. 
(c) Sclerenchyma may be found and studied (1) as the little 
“grit’’ bodies in the flesh of the pear or sapodilla (Achras 
sapota), (2) in the underground stem of the brake (Pteridium 
aquilinum), (3) next to the epidermis in the prickly pear 
(Opuntia), as well as (4) in coats of many seeds, e.g. apple, 
squash, wild cucumber, and (5) forming the body of the 
seeds of many palms, e.g. date. 
(d) Examine a young leaf-stalk of the squash or pumpkin 
and note the whitish bands, 1 or 2 mm. wide, which extend from 
end to end just beneath the epidermis. These are bands of 
collenchyma. They may be readily torn out, when the stalk 
will be found to have lost much of its strength. 
(e) Make a very thin cross-section of the leaf-stalk of one of 
the foregoing plants, exaetly at right angles to the axis of the 
collenchyma strands, and examine under low and high magnifi- 
cations. Test with iodine and sulphuric acid to determine the 
composition of the walls. 
(f) Make longitudinal sections through these collenchyma 
bands. If good sections are obtained the thickened ‘angles 
(becoming thin toward the point where the thin cross walls 
occur), chloroplasts and nuclei will be found. However, only 
