

37© Cooke and Schively on Observations on the 



ably only another of the degeneration effects due to para- 

 sitism. 



In a section through a mature stem just above the tuber, 

 the bundles form a quite regular narrow ring, its width 

 being less than one-sixth the entire diameter of the stem. 

 There were twenty-one separate bundles, varying greatly 

 in size. There is an average size presented by about two- 

 thirds of all the bundles. The remainder are mostly smaller, 

 some being mere rudiments of bundles, less than one-twen- 

 tieth the usual size. A few are larger than the average. 

 Frequently two bundles are seen fused together. 



An individual bundle is wedge-shaped in section, taper- 

 ing inward toward the pith. The outer area is formed of 

 hard bast cells, and is the most extensive cell area in the 

 entire bundle. It consists of cells with extremely thick 

 rounded cell walls and devoid of intercellular spaces. The 

 greater extent of the cell wall stains scarcely at all, and is 

 clear and refractive. The outermost layer stains deeply 

 with saffranin, looking like a fine red line passing around 

 the cell. It forms sharp angles at the cell intersections, 

 while the inner margin of the cell wall is perfectly round 

 and smooth. 



Below these bast fibres lies the true phloem, nearly equal- 

 ing them in amount. This region takes methyl green stain 

 exclusively in saffranin anilin green double stain, and is 

 characterized by protoplasmic, thin-walled delicate tissue. 

 There are numerous large rounded phloem cells, and scat- 

 tered among these are much smaller cells with a sharply 

 angular outline. These cells invariably contain a dense, 

 green-stained, balled-up mass. Their appearance is iden- 

 tically that of sieve-tubes in section, yet I have not been 

 able to assure myself of the presence of sieve-plates in the 

 longitudinal sections. It may be that degeneration has 

 caused the loss of these structures, while the cells that pos- 

 sessed them remain. 



The xylem cells lie next within, and are chiefly notable 



