2l6 



BOTANY. 



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. 192. The petiole now gradually straightens 

 up, and as it elongates the leaf expands. 



355. 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 would 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 compound leaves, a sort of recapitulation of 

 the evolutionary history of the leaf in these forms. 



