16 PRACTICAL COURSE IN BOTANY 
seeds by a slight roughness, is the chalaza, or organic base of 
the seed, where the parts all come together like the parts of a 
flower at their insertion on the stem. Where was it situated 
in the common bean? How does this differ from its 
position in the castor bean? Where the rhaphe ends, 
just at the beak of the caruncle, you will find the hilum. 
The micropyle is covered by the caruncle, which is an 
outgrowth around it. 
Now cut a vertical section through a seed that has been 
soaked for several days, at right angles to the broad sides, 
and sketch it. Label the white, pasty mass within the 
seed coats, endosperm. Can you make out what the narrow 
white line running through the center of the endosperm, divid_ 
ing it into two halves, represents? Make a similar sketch 
of a cross section. 
Notice the same 
white line running 
horizontally across 
the endosperm, di- 
viding it into two 
equal parts. To 
Fies. 20-22. — Castor bean (slightly magnified) ; 20, find out what these 
back view ; 21, front view ; ch, chalaza; r, rhaphe; ca, lines are, take an- 
earuncle ; 22, vertical section ; en, endosperm ; cc, cotyle- 
dons; hy, hypocotyl; hi, hilum ; m, micropyle. other seed (always 
use soaked seeds for 
dissection) and remove the coats without injuring the kernel. 
Split the kernel carefully round the edges, remove half the 
endosperm, and sketch the other half with the delicate em- 
bryo lying on its inner face. You will have no difficulty 
now in recognizing the lines in your drawings as sections of 
the thin cotyledons. Where is the hypocotyl, and which way 
does its base point? Remove the embryo from the endosperm, 
separate the cotyledons with a pin, hold them up to the light, 
and observe their beautiful texture. Sketch them under the 
lens, showing the delicate venation. Is there any plumule? 
Test the endosperm with a little iodine, Does it give a 
