178 EMBRYOLOGY. [CH. XIII 



The next stage of interest is shown in fig. 82, B 2, 

 where the embryo-cell at the lower end of the suspensor 

 has divided into eight cells, of which, however, only four 

 are visible. Of these eight cells, the four lower ones, i.e. 

 the four which make up the free rounded end of the embryo, 

 give rise to the cotyledons and plumule, while the four 

 next the suspensor give rise to the radicle. Thus when 

 the embryo consists of no more than eight cells, it is 

 possible to distinguish in it distinct morphological regions. 



In fig. 82, B 3, it will be seen that the lowest cell of the 

 suspensor h projects slightly into the spherical body of 

 the embryo. This projecting cell is called the hypophysis, 

 and its encroachment among the cells of the embryo 

 indicates its further history: for the hypophysis takes a 

 share in the architecture of the embryo, by dividing and 

 supplying a group of cells at the upper end of the embryo. 

 Thus the embryo-cell gives rise to plumule, cotyledons 

 and part of the radicle, while the hypophysis gives rise to 

 the tip of the root and the root-cap. In fig. 82, B, it may 

 be seen how the eight cells 1 , of which the embryo consists 

 in B 2, have produced curved superficial cells in B3: 

 these are the primary epidermic, or as they are called, 

 the dermatogen cells. The eight dermatogen cells give 

 rise by continued division to the superficial cells over 

 the whole of the plant, except in the region of the root 

 built up by the hypophysis. This is a good instance of a 

 "tissue by birth right 2 ," the epidermis comes to be one 

 of the fundamental divisions of plant-tissues because it 

 originates thus early in the history of the embryo. 

 1 Only four being visible. 2 See p. 37. 



