SEEDLINGS. 313 



590. If wc make a longiseclion of the embiyo and seed at this time we can 

 see how the club-shaped cotyledon is closely surrounded by the endosperm. 

 Through the cotyledon, then, the nourishment from the endosperm is readily 



passed over to the growing embryo. In the hollow part of the petiole near 

 the bulb can be seen the first leaf. 



591. How the first leaf appears. — Ab the embryo backs out of the seed, 

 it turns downward into the soil, unless the seed is so lying that it pushes 

 straight downward. On the upper side of the arch thus formed, in the 

 petiole of the cotyledon, a slit appears, and through this opening the first leaf 

 arches its way out. The loop of the petiole comes out first, and the leaf later, 

 as shown in fig. 409. The petiole now gradually straightens up, and as it 

 elongates the leaf expands. 



592. The first leaf of the jack-in-the-pulpit is a simple one. — The first leaf 

 of the embryo jack-in-the-pulpit is very different in form from the leaves which 

 we are accustomed to see on mature plants. If we did not know that it 

 came from the seed of this plant we should not recognize it. It is simple, 

 that is it consists of one lamina or blade, and not of three leaflets as in the 

 compound leaf of the mature plant. The simple leaf is ovate and with a 

 broad heart-shaped base. The jack-in-the-pulpit, then, as trillium, and some 

 other monocotyledonous plants which have compound leaves on the mature 

 plants, have simple leaves during embryonic development. The ancestral 

 monocotyledons are supposed to have had simple leaves. Thus there is in 

 the embryonic development of the jack-in-the-pulpit, and others with com- 

 pound leaves, a sort of recapitulation of the evolutionary history of the leaf in 

 these forms. 



