172 
PHARMACEUTICAL BOTANY 
which ere long attain the size of the first or primary root. The cau- 
licle, carrying upon its tip the plumule, elongates and forms the stem; 
the leaves of the plumule spread out and turn green to function as 
foliage leaves. The perforated cotyledonary sheath grows out sur- 
rounding both the root and the stem for a portion of their length. By 
this time all or nearly all of the nourishment stored in the endosperm 
has been absorbed and assimilated by the young seedling and the 
coat and scutellum, left behind, gradually decay and disappear. The 
root-hairs absorb nourishment from the soil, the green leaves build 
up carbohydrates, prop-roots make their appearance at the first 
node (joint) above ground, and the seedling grows larger. 
Gross Structure of a Dicotyl Seed, Phaseolus lunatus (Lima Bean). 
— The Lima Bean Seed shows a flattened-ovate to somewhat reni- 
form outline. Externally it exhibits a polished seed coat which is 
perforated on its basal side by a minute pore called the micropyle or 
foramen. Just below this pore will be noted the hilum or scar which 
represents the point of detachment from the funiculus or stalk which 
connected the seed during its growth with the wall of the fruit. 
Upon soaking the seed in water, it is possible to remove the seed coat 
or spermoderm. This done, the embryo will be exposed. The two 
fleshy cotyledons are first seen. Upon spreading these out, convex 
sides down, the rest of the embryo, consisting of a thin leafy structure 
surrounding a bud and called the plumule, the caulicle or rudimen- 
tary stem and in line with the latter, the radicle, or rudimentary 
root, will be seen. 
Histology of the Lima Bean Seed. — In transverse sections, the 
following microscopic structures will be evident: 
i. Spermoderm of three regions, viz.: Palisade cells, Column cells, 
and Spongy Parenchyma. The palisade cell layer is composed of 
vertically elongated thick-walled cells which are covered on their 
outer faces by a clear glistening cuticle. The cells are 60 to 8oyu long 
and 1 2 to 2o/x wide. The column cells, found forming a layer directly 
beneath the palisade zone, are hour-glass-shaped and 25 to 35^ long 
by 14 to 35 ju wide. 
The spongy parenchyma forms a zone of several layers of thin- 
walled parenchyma cells, the cells of the outer and inner layers being 
considerably smaller than the middle layers. 
