MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE. 173 



starch-ring. The xylem is unusually strong, as will be seen by the accompanying plate. 

 The woody fibres have apparently become stereids, mostly with tapering ends; the 

 cavities are either of about the same thickness of the walls or are nearly obliterated ; the 

 diameter ranges from 10-15 ^, and the length averages about 200 fi. The tracheides and 

 vessels extend throughout the collateral bundles, and sometimes even interrupt the 

 starch-ring; they vary from the same size as the woody fibres to 20 ft in diameter. Far 

 out in the xylem we meet with small annular vessels with very faint markings. Further 

 in come open spirals with stout markings, while still nearer the centre are close spirals 

 and tracheides with very small border-pits. 



The pith in this instance agrees well with that of section Avicularia, the cells being 

 many times longer than broad, measuring 10-30 ^ X 50-250 (i. 



SUBGENUS TINIARIA. 



Polygonum scandens. In place of an erect or prostrate stem, we have in this case 

 one which climbs by twining. The epidermis varies from 20-25 [i. The periblematic 

 cylinder is weak and reaches a thickness of only 50 fi. The plerome derivatives do not 

 exhibit any strong characters, and are from 25-45 {j. in thickness, excluding the pith. 



The epidermis consists of a single row of cells measuring from 60-110 jx, in length; 

 they are somewhat irregular in long section, especially about the ends, and in cross sec- 

 tion vary from nearly square to oblong, and are generally about 20-23 fz X 30-50 [i. 

 Trichomes in the shape of unicellular cones arise from the epidermis in such numbers as 

 to give it a scurfy appearance ; these hairs are not much elongated, and usually have an 

 erect tendency. Following this is the prinaary cortex, made up of irregular lenticular 

 cells, and in comparison with that of other subgenera poorly developed ; its depth never 

 increases to more than two cells, and these are only about 10 ff thick; their length and 

 breadth vary from 20-70 ^. The starch-ring is variable, in some cases, as represented 

 in the cross section figured, it is quite narrow and weak, while in others, as we see in the 

 long section, it is strong and regular. This is never more than one layer of cells, and 

 these are either irregularly prismatic or lenticular. 



Taking up the plerome derivatives, we meet with an extensive though structurally 

 weak development of sclerotic tissue. The stereids are, as usual, prismatic, measuring 

 from 20-70 (i in diameter and 250-400 (i in length, and lying in from three to five rows ; 

 the septa are transverse or oblique and the cavities large ; the structure differs in this 

 respect from that of all other subgenera, and the cell walls are seldom over 5 fi thick ; 

 they either come into contact with the xylem or phloem. In the stems sectioned this 

 latter tissue had fallen away, leaving only large cavities. The fascicles of phloem in this 



