164 



INTRODUCTION TO BOTANY 



155. Types of seedlings. Seedlings l 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, 

 should not be planted deep. Very minute 



FIG. 145. Pea seedling 



cot, the unopened cotyle- 

 dons ; GL, ground line ; r, 



root ; s, stem ; l, rudimen- seeds, like those of the portulaca, poppy, 



tary leaves^One half nat- and mogt plants Q f the p mk f amil ^ 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 

 and transfer it to the growing embryo. In such dicotyle- 

 donous seeds as those of the pea, horse-chestnut, and buckeye, 

 1 Not considering those of coniferous shrubs and trees. 



