232 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



of the zygote, results in the formation of a small micropylar and a 

 considerably larger chalazal chamber. Further divisions take place 

 in the micropylar chamber only (Fig. 128 A, B). In Balanophora, 

 where the sequence has been followed in greater detail, the micro- 

 pylar chamber (Fig. 128C) divides vertically to form two adjoining 

 cells enveloping the zygote (Fig. 128D). The second and third 

 divisions are transverse and result in four and eight cells respectively 

 (Fig. 12SE,F). The following divisions are less regular, but the 

 young embryo soon becomes surrounded by a number of small endo- 

 sperm cells. Later, owing to a further increase in the number of 

 endosperm cells and their enlargement, the large chalazal haus- 

 torium becomes squeezed and crushed. 



A very well developed and aggressive micropylar haustorium 

 occurs in Impatiens (Dahlgren, 19346). The first division of the 

 primary endosperm nucleus gives rise to two chambers (Fig. 129 A). 

 The micropylar chamber, which is the smaller, divides transversely 

 into three cells (Fig. 1295). The uppermost of these, containing 

 the zygote, forms a giant haustorium whose branching arms extend 

 as far as the funiculus (Fig. 129C-F). The next gives rise to a group 

 of cells which lie in close proximity to the young embryo. The 

 third, in which the divisions are not accompanied by wall formation, 

 fuses with the large chalazal chamber, which also contains only free 

 nuclei. Eventually cell formation takes place here also, but some 

 rounded masses of plasma, often containing several nuclei, seem to 

 become detached from the wall of the embryo sac and swim as "free 

 plasma balls" in the liquid below the cotyledons. 



Passing now to plants in which both micropylar and chalazal 

 haustoria are formed, we may first refer to the family Acanthaceae, 

 several members of which have been studied by Mauritzon (1934). 

 In Ruellia and most other genera the first division of the primary 

 endosperm nucleus cuts off a small chalazal haustorium with dense 

 cytoplasm, in which there are two nuclear divisions resulting in four 

 free nuclei (Fig. 1305). The micropylar cell divides transversely 

 to give rise to two daughter cells, of which the upper becomes bi- 

 nucleate and forms the micropylar haustorium (Fig. 130C). The 

 central cell, which is the largest, forms a sac-like outgrowth in which 

 there are several free nuclear divisions (Fig. 130D-G). A large 

 vacuole appears in the center of the cell, and the nuclei become dis- 

 tributed in the peripheral layer of cytoplasm, with a stronger 



