SEEDLINGS OF THE COMMON BEAN TYPE 107 
Onion Seedling.— The seedling of the Onion represents 
another type of monocotyledonous seedlings. In this type the 
hypocotyl elongates and pushes the cotyledon above ground. 
(Fig. 99.) As in the Grass seedlings, the primary root system 
is temporary —a feature quite common in Monocotyledons, al- 
though in some it lives much longer than in others. 
Seedlings of the Common Bean Type. — The seedling of the 
Common Bean is representative of those dicotyledonous seedlings 
in which the cotyledons through the elongation of the hypocotyl 
are carried above ground, sometimes several inches or even a 
foot in some Beans. Squashes, 
Cucumbers, Pumpkins, Melons, 
Radishes, Turnips, Castor Bean, 
Maples, Ashes, Clover, Alfalfa, 
etc., besides many of the Beans 
have this type of seedling. In 
seedlings of this type the first root 
system is usually the permanent 
one and soon firmly anchors the 
hypocotyl which then by an arch- 
ing movement pulls the cotyle- 
dons out of the ground in such a 
way that they offer the least re- 
sistance in passing through the Fic. 101. — Squash seed germi- 
soil and afford the most protec- nating, showing the peg by which 
tion for the delicate plumule. the seed coat is held while the 
(Fig. 100.) In some cases, as in cotyledons) ore pul ene of) ie 
fi seed coat by the arch of the hy- 
the Melons and Pumpkins, the pocotyl. Somewhat reduced. 
hypocotyl also assists in casting 
off the seed coat, in which case the arch of the hypocotyl pulls 
the cotyledons out of the seed coat while the latter structure is 
held in place by a peg-like structure of the hypocotyl. (Fig. 101.) 
In most cases, however, the seed coat is torn and gradually 
pushed off by the growth of the seedling. Since the first root 
system is usually the permanent one, its depth is closely related 
to the depth of planting. 
The plumule remains small and enclosed between the coty- 
ledons until pulled out of the soil. Then by a straightening of 
the hypocotyl arch and the spreading of the cotyledons, it is fully 
exposed to the light, where it develops all of the plant above the 
