MEMOIRS FEOM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE. 169 



oblique. The tubes are surrounded by accompanying tissue, whose length is several 

 times shorter than that of the former elements. A thick zone of xylem follows the 

 phloem. The woody fibres are small in cross-section (5-15 fi in diameter), oblong, with 

 the longer axes radial ; they are typical in all respects, and vary in length from 250-350 

 II. Small but distinct bundles exist between the large ones, and have their system of 

 tracheae and wood-parenchyma. Radially from the large bundles the phloem breaks 

 through the stereome cylinder, and meets the starch-ring, while radially from the small 

 bundles the starch-ring interrupts the stereome and comes into contact with the phloem. 

 An arrangement of the tracheides and vessels exists, different from that of the two pre- 

 ceding subgenera.- Instead of being situated about a line where the woody fibres and 

 wood-parenchyma respectively predominate, they are scattered throughout the bundles. 

 We meet few tracheides, but numerous vessels. The former have small diamond-shaped 

 markings, and the latter various kinds of spirals. Only a few annular markings were 

 observed in the sections cut, and these were connected with either single or double spirals. 

 Toward the outside of the bundles rather open and double spirals occur, and further in 

 come the close and open single spirals; the latter and the double open spirals seem to 

 be stouter than the others. Wood-parenchyma and intermediate tissue constitutes the 

 bulk of the inner sides of the bundles, and are arranged so that in cross section they 

 appear as flat semicircular projections into the pith. 



The pith is diflferent from that described under the two preceding subgenera. After 

 passing a row of more or less elongated parenchymatous cells, we find it made up of nearly 

 isodiametric elements, although in the young state they may be mu.ch longer than broad. 



SUBGENUS TOVARA. 



Polygonum Virginianum. . A plant somewhat resembling the preceding and called 

 on to bear about the same kind of a strain by the branching of its summit into long 

 virgate racemes which, unless properly supported, would bear down the main axis. We 

 find the general structure of this stem much the same as that of P. Pemisylvanicum, 

 the epidermal and periblematic cylinders are not as thick (50-100 fi), but the plerome 

 derivative is much thicker, running as high as 500 fi. 



The cells of the epidermis are small parallelopipeds, ranging from 5-20 ^ in diame- 

 ter and from 10-20 fi in height. 



The primary cortex appears normal in cross section, the cells, excepting those of the 

 starch-ring, varying from 10-20 fi in diameter and are three or four layers thick; they 

 are quite rectangular in outline, and only prismatic near the starch-ring. In long section, 

 however, they are extraordinary, appearing almost like fibres and measuring from 250- 



