THE EMBRYO 



2*3 



tmbryo now comprises five tiers (excluding cb), namely n' , n, m, V , 

 and I. The next division is also vertical (at right angles to the first) 

 in I, V, and m, and results in the formation of three quadrants; n 

 also divides by a vertical wall; and n' divides by a transverse wall 

 to give rise to o and p (Fig. 156G,H). Of the six tiers formed in 

 this way, I is destined to give rise to the stem tip, V to the cotyledons, 

 m to the hypocotyl, n to the root cap, and o and p to a short sus- 

 pensor which abuts on the large cell cb. 



Fig. 157. A-H, development of embryo in Sediwi acre; cells marked end belong 

 to endosperm and ch is the chalazal haustorium. (After Soueges, 1927.) I, l.s. 

 portion of ovule, showing haustorial processes formed from basal cell of proembryo. 

 (After Mauritzon, 1933.) 



Sedum acre (Soueges, 1927, 1936c?) resembles Sagina in having a 

 large and undivided basal cell (cb), but in other respects the develop- 

 ment shows some differences. The terminal cell ca, which is small 

 and lenticular, divides transversely into two superposed cells, of 

 which the upper again divides transversely (Fig. 157 A, B). Of the 

 resulting four cells, cc undergoes two vertical divisions to form 

 quadrants (Fig. 157 D,E) and then a transverse division to form 

 octants (Fig. 157 F) ; m divides transversely into two flattened cells 

 h and/, the former of which constitutes the hypophysis (Fig. 157i?) ; 

 ci becomes partitioned by vertical walls to form four juxtaposed 

 cells which do not divide again but become greatly flattened and 

 form a short suspensor (Fig. 157C-H); cb forms an aggressive 

 haustorium whose branches penetrate the seed coat (Fig. 157/). 



