68 



ESSENTIALS OF BOTANY 



Examine a vegetable sponge (Luffa), 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 singlfe kind of stem. Examine (a) the cork 



Fig. 39. Diagrammatic Cross-Section of an Annual Dicotyledonous 

 Stem. (Somewhat magnified.) 



p, pith ; fv, woody or fibro-vascular bundles ; ti, epidermis ; 6, bundles of 

 hard bast fibers of the bark. 



Fig. 40. Diagrammatic Cross-Section of One- Year-Old Aristolochia 

 Stem. (Considerably magnified.) 



e, region of epidermis; 6, hard bast; o, outer or bark part of a bundle 

 (the cellular portion under the letter) ; w, inner or woody part of 

 bundle; c, cambium layer; p, region of pith; !?i, a medullary ray. 



The space between the hard bast and the bundles is occupied by thin- 

 walled, somewhat cubical cells of the bark. 



