360 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



regarding it as a reduced apetalous and polygamous or dioecious 

 derivative of the latter. 



That this last view is the correct one and that the Empetraceae 

 is to be classed under the Ericales have now been definitely estab- 

 lished on the basis of the embryological data brought forward by 

 Samuelsson (1913). This order is characterized by the following 



D 



Fig. 198. Development of endosperm in Empetrum nigrum. A, embryo sac at 

 time of fertilization. B, two-celled stage of endosperm. C, four-celled endosperm. 

 D, more advanced stage, showing differentiation of micropylar and chalazal haus- 

 toria. E, l.s. nearly mature seed. (After Samuelsson, 1913.) 



well-marked embryological features: (1) absence of a fibrous layer 

 in the anthers ; (2) anther tapetum of the glandular type with multi- 

 nucleate cells; (3) microspores remaining together in tetrads (Fig. 

 97/) ; (4) pollen grains two-celled ; (5) unitegmic ovules with a thin 

 nucellus, which soon disappears so that the embryo sac comes in 

 direct contact with the integumentary tapetum; (6) absence of 



