Origin and Development of the Composite. 145 
II, 63), and the primitively lateral position of the ovule isconfirmed 
by the anomalous cases figured by the writer (99) in which all the 
four lateral ancestral placentae of the two carpels are indicated. 
The single archesporial cell is differentiated at an early stage 
as the end cell of a row in the middle of the young ovule (Pigs. 56- 
57). The integument shows an unilateral development almost from 
its first appearance (Figs. 56-58). While reduction division is 
taking place, the integument develops very rapidly, so that the 
following stages occur within a single-layered nucellus enclosed by 
the integument with its peculiar epithelium. A row of four 
megaspores is formed, with the middle or first formed wall very 
thick (Figs. 59-60). This wall disappears and the two middle 
megaspores degenerate (Fig. 61); the apical megaspore also degener¬ 
ates and the basal one develops into the embryo sac (Fig. 62). 
Palm (84) considers that in Solidago and Aster the sac is formed 
from the micropylar megaspore and that the three lower 
megaspores develop into the haustorium. He is, however, adversely 
criticised by Chamberlain (49); and most other workers on the 
embryo sac of the Compositae agree in describing the sequence of 
events as above. 
This question has recently become rather controversial. 
Holmgren (64) describes six methods of embryo sac development 
in the Compositae. 
A. with a row of four cells as megaspores, 
(1) . Sac from the chalazal megaspore, normal and eight- 
nucleate, as in most cases (69, 77, 91, 93, etc.); 
(2) . Sac from one of the other three megaspores and not 
always eight-nucleate, as in Senecio vulgaris (Winge, 
113), Solidago serotina and Aster uovce-anglice (Palm, 
84), all three species with persistent megaspores in the 
antipodal region. 
B. With only one wall formed after the heterotypic nuclear 
division, 
(3) . Sac from the two micropylar megaspores, as in 
Tamicetum vulgare (Palm, 85); 
C. With no wall formed during meiosis ; 
(4) . Sac from the micropylar megaspore nucleus and 
eight-nucleate, as in Anthemis tinctoria (Holmgren, 
64); 
(5) . Sac from the two micropylar megaspore nuclei and 
eight-nucleate with persistent chalazal megaspores 
as in Tanacetum vulgare (Palm, 85); 
