Flahault.* A heel or peg is developed on one side of the
summit of the radicle or base of the hypocotyl; and this holds down the
lower half of the seed-coats (the radicle being fixed into the ground)
whilst the continued growth of the arched hypocotyl forced upwards the
upper half, and tears asunder the seed-coats at one end, and the cotyledons
are then easily withdrawn.
Fig. 62. Cucurbita ovifera: germinating seed, showing the heel or peg
projecting on one side from summit of radicle and holding down lower tip of
seed-coats, which have been partially ruptured by the growth of the arched
hypocotyl.
The accompanying figure (Fig. 62) will render this description
intelligible. Forty-one seeds of Cucurbita ovifera were laid on friable
peat and were covered by a layer about an inch in thickness, not much
pressed down, so that the cotyledons in being dragged up were subjected to
very little friction, yet forty of them came up naked, the seed-coats being
left buried in the peat. This was certainly due to the action of the peg,
for when it was prevented from acting, the cotyledons, as we shall
presently see, were lifted up still enclosed in their seed-coats.
Pages:
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186