58 PHARMACEUTICAL BOTANY 
Since the xylem is surrounded by the phloem, the vascular bun- 
~ dle is of the xylocentric type. Strictly speaking, the endodermis 
and pericambium are accessory regions, surrounding, but not 
part of the bundle proper. 
HisroLocy or Growinc ApEx.—When the bases of the leaves 
of the current year, the young rolled up leaves of the following 
year and the large mass of brown scales have been removed 
from around the apical bud of a well-grown plant, the following 
structures may readily be observed with a hand lens: 
1. The ApicaL Cone (punctum vegetationis), a rounded papilla, 
which occupies a terminal position in the apical region. 
Fic. 31,—Apical cell of a fern rhizome in vertical longitudinal section. 4.¢., 
apical cell; 4, hair; m, meristem, (After Hofmeister.) Sedgwick @ Wilson’s General 
Biology, Henry Holt & Co. - : 
2. The Younc Fronps, arranged around the apical cone. 
Upon removing the extreme apex of the apical cone with a 
sharp razor, mouting in dilute glycerine or water and examining 
under low power, it will be noted that a large pyramidal cell 
occupies the center of the apical cone. This is the apical cell 
(Fig. 31). The cells surrounding it have been derived by 
segmentation (cell-division) from it, by means of walls parallel 
to its three sides; they are termed segment cells and in turn undergo 
further division and redivision to originate the entire stem tissue 
and leaf tissue. Step by step the tissue cells become modified into 
epidermal, cortical, bundle and fundamental cells. 
HisroLocy or Mature Roor.—Transverse sections cut some 
distance above the root apex will present the following structures 
for examination: (See Fig. 32). 
