8 SOUTH AFRICAN BOTANY 
covering being the pericarp (fig. 5). Inside this is the 
seed surrounded by a thin yellowish membrane, the testa. 
It is exendospermous, the whole seed forming the 
embryo. It can be readily split into two cotyledons, 
the plumule lying between them. The pointed end of 
the seed is a radicle. 
During germination the radicle elongates and then 
that part of the radicle immediately below the cotyledons, 
scar where 
cotyledons” 
ploy 
Fic. 4.—The Germination of the Mustard Seed. 
known as the Hypocoryt, elongates and bends to form 
a loop. It emerges through the soil in this form and 
then drags the cotyledons out of the seed-case and lifts 
them above the ground, where they turn green and act 
as the first leaves. Sometimes the seed-case is carried 
above ground by the cotyledons, but soon drops off on 
their continued growth. This method of drawing the 
cotyledons above the soil is one often employed by 
dicotyledonous seeds, as obviously there is less danger 
to the delicate plumule than there would be by direct 
growth upwards. 
