MEMOIRS FEOM THE DEPARTMENT OP BOTANY OF COLUMBIA COLLEGE. 165 



THE COMPARATIVE ANATOMY. 



The following examples have been selected as being most typical of the subgenera 

 they respectively represent. In the case of subgenera that contain few and similar spe- 

 cies, the anatomical structure of the type selected seems to be fairly constant. On the 

 other hand, in the large subgenera which contain numerous species diflPerent in appear- 

 ance and either erect or prostrate in habit, we cannot hope to find the structure very 

 uniform. Therefore, in any conclusions reached in this study as regards subgenera, this 

 fact must be considered. The comparisons as recorded below may be regarded as nearly 

 correct, for the material studied was taken from practically the same portion of the stem 

 in each case, and is almost without exception of about the same age. 



SUBGENUS BISTORTA. 



Polygonum bistortoides. We are here concerned with an erect unbranched axis. 

 The stem is rather rigid and has to support its leaves and terminal raceme as well as to 

 maintain its erect position. The epidermis averages about 12 ju, and the periblem de- 

 rivatives measure from 25-95 /j.. The pleromatic cylinder is strong, the stereome ele- 

 ments forming a continuous sheath ranging from 40-100 n, while the xylem attains a 

 maximum diameter of 150 (i. 



The epidermis is simple, its cells being parallelepipeds or prisms, sometimes meas- 

 uring 15 fiX 10-20 fi broad and 40-70 fj. high. Their septa are either square or a little 

 oblique, and in cross section they vary either way from equilateral. Trichomes exist as 

 elongated unicellular hairs with blunt apices. On the stem they are found only on the 

 younger parts about the inflorescence and are non-glandular. 



The next zone, the primary cortex, is clearly marked off from the epidermis. In 

 many instances the cells of the hypoderma are only one-half as large as the overlying 

 ones and vary from somewhat prismatic to lenticular-vermiform. They lie in two to 

 seven rows, and have these dimensions: 5-10 ^ X 10-20 ^ X 30-40 fi. The starch-ring 

 follows and normally consists of a single layer of cells which are larger than those of 

 either of the outer tissues; their shape is mostly oblong and their size 12-25 ^ X 15-30 



fi X 40-95 fi. 



A wide zone (40-100 fi) of sclerenchymatic cells begins the pleromatic cylinder. 

 The cells are prisms, ranging from 10-30 (i in diameter, and from 150-330 ^ in height. 



