156 BOTANICAL GAZETTE [august 



Trifolium pratense 



A more thorough study was made of 

 economic importance, and it was hoped 

 its moroholosrv would aid in controlling 



The 



discussion of Trifolium pratense will be somewhat detailed, and 

 will form a basis for a comparative treatment of the other 4 



species 



campy 



are attached to a cushion-like placenta (fig. 1). The outer in teg- 



which is barely a distinct ridge when the inner appears, 



ument 



forms a heavv rim 



(figs. 8, 10). The outer integument, which varies from 2 to 4 



thickness 



many 



and the outer row of cells forms the peculiarly thickened and 

 cutinized layer of the testa. The inner integument usually remains 



mbryo sac. Some 



times 



hemispherical at the time 



be identified, but elongates rapidly and is quite slender at the time 

 the embryo sac is mature (fig. 12). There are usually 3 sub- 

 epidermal rows (fig. 3), but often 3-6 rows are found at the base of 

 the nucellus (fig. 12). 



Embryo sac. — From 1 to 4 archesporial cells were observed. 

 and more than half of the ovules showed more than one archesporial 

 cell. In fig. 3 there are 4 archesporial cells in a longitudinal row. 

 In fig. 4 there are 4, but 3 are hypodermal and the other is more 

 deeply placed. In either case, it is probable that the 4 archesporial 

 cells have come from the division of a hypodermal cell at an early 

 stage in the development of the nucellus. It is also probable that 

 the cells deeper than the hypodermal layer may become sporoge- 

 nous. One parietal cell is cut off (fig. 2), which usually divides 

 transversely to form a longitudinal row of 2 or 3 cells (fig. 8), or 

 one transverse and one longitudinal division may occur (fig. 6). 

 No division (fig. 7) or only a longitudinal division has been observed. 

 In fig. 5 two of the three megaspore mother cells have reached the 

 synapsis stage, but more than one row of megaspores was not found. 



