68 ESSENTIALS OF BOTANY 
Examine a vegetable sponge (Lujfa), sold by druggists, and notice 
that it is simply a network of fibro-vascular bundles. It is the skele- 
ton of a tropical seed-vessel or fruit, very much like that of the wild 
cucumber common in the Central States, but a great deal larger. 
The different layers of the bark cannot all be well recognized in 
the examination of a single kind of stem. Examine (a) the cork 
Fic. 39. Diagrammatic Cross-Section of an Annual Dicotyledonous 
Stem. (Somewhat magnified.) 
Pp, pith; fv, woody or fibro-vascular bundles; e, epidermis; 6, bundles of 
hard bast fibers of the bark. 
eb c Pp 
Fig. 40. Diagrammatic Cross-Section of One-Year-Old Aristolochia 
Stem. (Considerably magnified.) 
e, region of epidermis; 6, hard bast; 0, outer or bark part of a bundle 
(the cellular portion under the letter); w, inner or woody part of 
bundle; ¢, cambium layer; p, region of pith; m, a medullary ray. 
The space between the hard bast and the bundles is occupied by thin- 
walled, somewhat cubical cells of the bark. . 
