DESCRIPTION OF PLATE IV. 



Cross section of a mature watermelon stem, showing how the vessels are plugged 

 by the fungus. In this stage of the disease the foliage has suddenly wilted (as 

 shown in PI. VII, 1), but is not yet shriveled; the stem is green and turgid and its 

 parenchyma is not yet invaded. From the surface inward the tissues are as follows : 

 (1) Epidermis, (2) coUeuchyma, (3) cortical parenchyma, (4) bast fibers (stereome), 

 (5) medullary system, (6) ten bicollateral bundles in two rows, (7) pith. The struc- 

 ture of the bundles is as follows : (1) outerphloem, (2) cambium, (3) xylem, consisting 

 of pitted and reticulated vessels held together by wood parenchyma, (4) spiral 

 vessels lying in non-lignified living parenchyma (the primary vessel parenchyma of 

 Strasburger), (5) pseudocambial layer, (6) inner phloem, composed like the outer 

 phloem of sieve tubes and companion cells. On the outer side of the outer phloem 

 may be seen the collapsed remnants of the primary sieve tubes. The middle portion 

 of the stem is occupied by fissures. Section embedded in paraffin, cut on the 

 microtome, and stained in hsematoxylin. Reduced one-third from a pen drawing 

 made directly from the section by Mr. W. Scholl. Diameter of the stem, 4 millimeters. 

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