PLANT ORGANS AND ORGANISMS 
217 
with an accompanying release of energy, which latter is necessary to 
life and growth. 
The combined pericarp and spermoderm bursts opposite the tip of 
the radicle, and the radicle, piercing through the cotyledonary sheath, 
protrudes. The cleft in the coat lengthens to the point opposite the 
tip of the plumule, which also protrudes after bursting through the 
cotyledonary sheath. The radicle, next, grows downward into the 
soil forming the primary root, and develops upon itself secondary or 
lateral roots, all of which give rise to root-hairs just above their root 
caps. Additional lateral roots emerge above the scutellar region 
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 ox 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: 
