322 PHARM ACEUTICAL BOTANY 
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. 
2. Empryo, the two cotyledons of which make up the greatest 
bulk. These are composed of an epidermis covering over a 
region of mesophyll. ‘The mesophyll is constituted of moderately 
thick-walled cells which contain ellipsoidal and kidney-shaped 
starch grains up to 65u in length. A conspicuous branching 
cleft will be seen in the larger grains. 
In the Lima Bean, the nourishment is stored in the embryo 
during the growth of the seed. It is, therefore, exalbuminous. 
GERMINATION OF Dicotyt SEEDs.—Following the imbibition 
of water and swelling of the seed contents, in dicotyledonous 
plants the hypocotyl is generally the first part of the embryo to 
elongate and emerge from the seed coat. Responding positively 
to the stimulus of gravity, it grows directly toward the center of 
the earth and enters the soil, becoming the primary root. The 
primary root continues to grow in the soil and ere long develops 
secondary roots. In the seeds of the Lima and other beans, the 
cotyledons and epicotyl are pulled above the soil by the elonga- 
tion of the hypocotyl which makes a crook. In seeds of the pea 
and corn, etc., in which the cotyledons or cotyledon remain 
within the seed coat under the ground, the elongation of the 
epicotyl brings the aerial organs above the soil surface. 
