432 BOTANICAL GAZETTE [may 



endospemi formation the tapetum appears to be very active. 

 Integumentary cells in contact with it are broken down and the 

 tapetal cells are always filled with a dense protoplasm. 



Haustoria 



With the formation of the endosperm 2 large haustoria are 

 formed: one in the neck which connects the micropylar and 

 chalazal ends of the sac (fig. 8), the other as an outgrowth from the 

 chalazal end of the sac (fig. 9). The former is formed by the growth 

 of 2 endosperm cells forward through the narrowed neck and just 

 into the micropylar end of the sac where growth stops. In the 

 case of the chalazal haustorium there is an outgrowth of the sac in 

 the region not covered by the tapetum. Into this bulbous pocket 

 4 endosperm cells grow. This brings the endosperm cells well 

 into connection with the vascular tissue, the cells of which are 

 gorged with nutritive material. The protoplasm of each haus- 

 torium is very dense. The cells of the chalazal haustorium are 

 binucleate. 



The active tapetal layer covers only the chalazal end of the 

 sac (fig. 8), ending abruptly at its junction with the micropylar 

 end. ScHMiD found that the tapetum might cover all of the 

 embryo sac or only part of it as in P. secundiflorus. The latter 

 condition seems the more common occurrence. Miss Mitchell 

 found that no tapetum is formed in Striga lutea. She believes that 

 this may be accounted for by the semi-parasitic habit of the plant. 



Development of embryo 



After fertilization the egg rests for a time, often even until 

 endosperm cell walls have begun to form. It then divides, the 

 first division being at right angles to the axis of the embryo sac. 

 The segment nearest to the micropyle forms the suspensor, the other 

 forming the embryo. By a series of divisions, coupled with rapid 

 growth, the suspensor is transformed into a bulbous basal portion, 

 and a number of smaller narrowed cells which lengthen rapidly in 

 such a manner as to push the i -celled embryo through the micro- 

 pylar end of the sac (fig. 8) and into the center of the endosperm 

 beyond (fig. 10). It is usually pushed from one-third to one-half 



