158 PHARMACEUTICAL BOTANY 
grown in forest or moor soil, this species has reddish flowers but 
when grown in soil containing pent aluminum compounds, its 
flowers are blue. 
REGIONS OF THE Root. vee are five regions of a root 
beginning with the extreme tip and passing backward. These 
are the root cap, the embryonic region, the region of elongation or growth 
in length, the region of maturation or cell differentiation and the 
mature region (see Fig. 94). These phases of growth can be seen 
in fixed and stained longitudinal sections of root tips. 
Root Cap.—The tip of each root or rootlet is protected by a 
smooth, sheath- or scale-like covering known as the root cap or 
calyptra. ‘This is a mass of cells which not only protects the 
delicate cells of the embryonic region but serves as a mechanical 
aid as the root pushes its way through the soil. 
Empryonic Recion.—This region is composed of small, 
densely arranged, somewhat polyhedral or quadrangular cells 
which undergo repeated division. ‘This region is about a milli- 
meter in length. 
Growinc Point.—The growing point of the root of a seed 
plant consists of a group of actively dividing cells directly beneath 
the rootcap. These cells make up the tissue called the primordial 
meristem. 
Primary MErIsTEMS.—Just in back of the primordial meris- 
tem, the cells have begun to show differentiation into three 
groups of tissues called primary meristems or generative tissues. In 
the posterior part of this region the cells gradually cease their 
rapid division and become larger due to the absorption of soil 
water. 
GENERATIVE TissuEs.—The generative tissues directly back of 
the growing point are, passing from the center toward the out- 
side: plerome or procambium, producing fibro-vascular tissue (xylem 
and phloem) and pith; pertblem or ground meristem, producing 
cortex including endodermis, and pericycle; and dermatogen or 
protoderm, producing epidermis. The name ca/yptrogen has been 
given to those cells of the primordial meristem which form the 
root cap. (Cf. Fig. 93.) 
RecIon oF ELoncAtion.—This region occurs just behind the 
embryonic region where the cells enlarge chiefly inlength. Root 
