164 INTRODUCTION TO BOTANY 
155. Types of seedlings. Seedlings! may be divided into 
two groups, monocotyledonous seedlings and dicotyledonous seed- 
lings. Those of the dicotyledonous group may be further sub- 
divided into plants with underground cotyledons, as the pea and 
the oak, and those with aboveground cotyledons, as the maple, 
bean, squash, and morning-glory (fig. 144). 
The monocotyledonous seedling may or may not raise its 
single cotyledon out of the ground after germination. The 
onion does so, but the grains do not. In 
all the larger grains (as in corn) the 
fitness of the plumule for piercing hard 
clods or bits of sod is very noticeable 
and frequently serves the plant well in 
breaking its way out of the ground. 
Dicotyledonous seedlings with under- 
ground cotyledons, like the pea (fig. 145), 
are better able to force their way out of 
the ground, if planted deep, than are 
most of those with aboveground cotyle- 
dons, like the bean. Therefore even large 
seeds of the latter type, like those of 
the bean, melon, cucumber, and squash, 
cae ase tales should not be planted deep. Very minute 
root; s, stem; /, rudimen- Seeds, like those of the portulaca, poppy, 
Hay saeaehi he oe half nat- and most plants of the Pink family, should 
be planted on the surface of well-raked, 
fine earth and then barely covered by sifting over them a 
little of the finest loam or by dragging a trowel or other 
suitable implement lightly back and forth over the bed. 
156. What becomes of the cotyledons. In the seeds of many 
monocotyledons, as in the grains and in date seeds, the coty- 
ledon is merely an absorbing organ ; it remains within the seed 
and serves to remove liquefied plant food from the endosperm 
an transfer it to the growing embryo. In such dicotyle- 
donous seeds as those of the pea, horse-chestnut, and buckeye, 
Fie. 145. Pea seedling 
' Not considering those of coniferous shrubs and trees, 
