214 Cook : Potamogeton lucens 



ipL 



Coker 



(3) describes a somewhat similar condition for certain of the Pon- 

 tederiaceae except that he describes the daughter-nucleus in the 



* 



antipodal end of the sac as going through a series of divisions to 

 form an endosperm. Campbell (1) reports the presence of a large 

 cell in the antipodal end of the embryo-sacs of Naias flexilis and 

 Zannichellia palustris but did not determine its origin in either case. 

 However, he states that this cell does not divide, but that in Zan- 

 nicJiellia palustris "it looked as if it were undergoing disintegra- 

 tion,' ' and that in both plants the endosperm arises in the synergid 

 end of the sac. Hall (8) in his studies on Limnocharis emarginata 

 reports a single antipodal cell and a single polar cell which is 

 formed in the micropylar end of the sac ; this single polar cell 

 divides and behaves in the same manner as the primary endosperm 

 in the Nymphaeaceae, Sagittaria, and Potamogeton lucens. This 

 embryo-sac is so remarkable in character and so unlike any other 

 known at this time, while the behavior of the polar nucleus is so 

 similar to the primary endosperm of the plant just referred to, that 

 one is justified in saying that the union of the two polar nuclei 

 may have been overlooked. Wiegand (14) in his studies of Pota- 

 mogeton foliosus describes a peculiar seven-nucleated sac. in which 

 but three nuclei (the egg and the two synergids) are formed at the 

 micropylar end of the sac, the polar nucleus from the antipodal 

 end of the sac dividing and behaving similarly to the primary endo- 

 sperm-nucleus in Nymphaeaceae, Sagittaria, and P. lucens. Hol- 

 ferty (9) in his studies of Potamogeton natans describes a normal 

 eight-nucleated sac. He failed to find a wall across the sac at any 

 stage of its history. He did not trace the development of the 

 endosperm but reports a very large nucleus near the antipodal end 

 of the sac, concerning which he says " Its origin could not be 

 determined, but it seems reasonable to consider it a derivative of 

 the primary endosperm-nucleus, and possibly the lower nucleus of 

 the first division, as in Sagittaria and Potamogeton paucifloras." In 

 the light of these later studies it seems possible that Wiegand may 

 have overlooked the formation of the eiirht-nucleate sac. Aside 

 from the fact that the antipodal cells of Potamogeton foliosus are evi- 

 dently more persistent than those in P. lucens, his figure 20 corre- 

 sponds quite well with figures* and 6 of this paper, his figure 21 with 



