THE EMBRYO AND SEEDLING 129 



leaves of the plant. Consequently only a small portion 

 of the fertilized egg takes part in the formation of the 

 plant, the greater portion being used as nutrition and 

 in the formation of the suspensor and haustorial cells. 



The region at the tip of the suspensor, which might 

 be called the embryo proper, since it will give rise to the 

 root, stem, cotyledons, and leaves, advances into the 

 endosperm, partly by digesting and absorbing the sur- 

 rounding cells, and partly by the crushing thrust of the 

 big suspensor. Cell division proceeds rapidly, so that 

 the advancing embryo soon consists of thousands of 

 small cells. 



Differentiation of the embryo takes place imper- 

 ceptibly. It is soon noticed that the rapid growth is 

 becoming somewhat retarded at the extreme apex, while 

 the growth of the region about it not only continues but 

 is even accelerated, thus causing a depression surrounded 

 by a ring of tissue. The ring is not entirely complete, 

 consisting of two equal crescentic portions nearly touch- 

 ing each other at their ends. The depressed area is the 

 stem tip; the two crescentic portions represent the 

 beginnings of the two cotyledons. The origin of the 

 root is difficult to detect, but converging rows of cells 

 soon indicate that the root region has been estabhshed 

 (Fig. 69). Even at the stage shown in this figure the 

 "dermatogen," which gives rise to the single-layered 

 epidermis, has not become differentiated, as those who 

 are students of morphology will recognize from the 

 pericUnes in the outer layer of cells. 



Soon after the two cotyledons are outlined, the ring 

 of rapidly growing tissue surrounding the stem tip 

 becomes complete, so that the two cotyledons are carried 



