218 Cook: DEVELOPMENT OF EMBRYO-SAC AND EMBRYO 
ever, the development of the embryo-sac bears a striking resem- 
blance to Potamogeton, Naias,and Sagittaria. The formation of 
tapetal cells and of megaspores is very similar to that described by 
Holferty for Potamogeton (8) and Campbell for Matas (4). The 
first division of the definitive nucleus and the formation of the wall 
across the sac is the same as observed by Schaffner in Sagittaria 
(12). 
Lyon concludes that -the Nymphaeaceae should be classified 
among the Monocotyledons in the series Helobiae (Naiadales). 
Van Tieghem in ‘‘ Elements de Botanique’’ (14) makes a special 
class including the Nymphaeaceae and Gramineae between the 
Monocotyledons and the Dicotyledons which he calls ‘‘ Liorhizes 
Dicotylees.’” Taking into consideration the general anatomy and 
habits of the plants, and the fact that the formation of a lower 
endosperm nucleus is similar to Sagittaria (12), it appears that the 
Nymphaeaceae should be placed in or near the order Naiadales. 
SUMMARY 
1. The archesporial cell is hypodermal. 
2. The formation of the tapetal cells is irregular. 
3. The formation of the megaspores is after the usual manner. 
4. The embryo-sac usually contains starch in the one-, two-, 
and four-celled stages. 
5. The formation of the eight-celled embryo-sac is in the usual 
manner. 
6. At least one of the synergids persists for a very long period. 
7. The antipodals are very small and disappear early. 
8. The endosperm nucleus divides and a wall is formed across 
the embryo-sac between the two nuclei. The upper forms true 
endosperm, the lower a tube extending to the chalazal end of the 
ovule for absorbing the cells of the nucellus. 
g. The embryo is at first spherical and later forms 4 single 
cotyledon. 
10. The suspensor is late in forming and apparently without 
function. 
11. The family Nymphaeaceae should be placed in or near the 
order Naiadales. 
The writer wishes to express his thanks to Professor J. Me 
