142 



PRACTICAL BOTANY 



G-- 



and those with aboveground cotyledons, as the maple, bean, 

 squash, and morning-glory. 



The monocotyledonous seedling may or may not raise its 

 single cotyledon out of the ground after germination. The 

 onion does so (Fig. 127) but the grains do not (Figs. 130, 131). 

 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 

 serves the plant well in breaking out of 

 the ground against opposition. 



Dicotyledonous seedlings with under- 

 ground cotyledons, like the pea (Fig. 

 132), are better able to force their way 

 out of the ground if planted deep than 

 are most of those with aboveground coty- 

 ledons, like the bean (Fig. 133). There- 

 fore even large seeds of the latter type, 

 like those of the bean, melon, cucumber, 

 and squash, should not be planted deep. 

 Very minute seeds, like those of portu- 

 laca, poppy, and most plants of the Pmk 

 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. 

 133. Function of the cotyledons. In many seeds of mono- 

 cotyledons, as the grains, the cotyledon does not emerge from 

 the seed nor rise above the surface of the ground. It forms an 

 absorbing organ known as the scutellum (Fig. 129, sc), which 

 serves to take up liquefied plant food from the endosperm and 

 transfer it to the growing embryo. In the seed of the date 

 palm it acts much in the same way. Other monocotyledonous 

 plants, like the onion, bring the cotyledon out of the ground 

 (often with the seed coat attached) and then proceed to de- 

 velop ordinary foliage leaves (Fig. 127). 



Fig. 132. Pea seedling 



cot, the unopened cotyle- 

 dons ; GL, ground line ; ?•, 

 root ; $, stem ; I, rudimen- 

 tary leaves. One half nat- 

 ural size 



