136 A. H. Graves, 



Before I leave the account of the megasporangium, two cases in 

 which the archesporium was undoubtedly two-celled should be 

 recorded. Murbeck (1902, p. 11 and figure 35) has figured a double 

 megaspore mother-cell, which, however, according to his explanation, 

 is caused by the very oblique orientation of the wall between 

 primary parietal and primary sporogenous cells, making this wall 

 almost perpendicular to the epidermis and hence resulting in two 

 large cells, apparently both potential megaspore mother-cells, and 

 bounded exteriorly by the epidermis. 



But my first illustration (PI. XI, fig. 77) shows a clearly differ- 

 entiated, single, parietal layer and two large megaspore mother- 

 cells with their common wall very distinct and quite perpendicular 

 to the epidermis. The second example has developed somewhat 

 further (PI. XI, fig. 78), the two megaspore mother-cells having 

 passed through the first division, a cross wall being formed, which 

 divides each into two essentially equal daughter-cells. Here may 

 also be noted the rather uncommon occurrence of two parietal layers. 



On the analogy of the microsporangium of Angiosperms, it would 

 seem most natural that multicellular archesporia should occur also 

 in the megasporangium. Through the investigations of Strasburger 

 (1879), Fischer (1880), and among others, especially Pechoutre (1902), 

 we have come to know that such a multicellular archesporium is 

 quite general in the megasporangia of the Rosaceae; and that it 

 also occurs in many other dicotyledonous groups has been sufficiently 

 proven. 



On the other hand, the reports of an archesporium of more than 

 one cell in the megasporangium of monocotyledons are meagre, 

 and, as reviewed by Coulter and Chamberlain, may be embraced 

 in two cases, Ornithogalum pyrenaicum (Guignard, 1882), and 

 Liliuni candidiim (Bernard, 1900). In these instances the archesporium 

 is presumably always more than one-celled. There are, however, 

 many cases, such as some of the Ranunculaceae, when the archespo- 

 rial cells vary from one to many (Mottier, 1895, and Coulter, 1898). 

 To such as these last the condition in Ruppia maritima is similar. 



Female Gametophyte 



As it is now regarded, the history of the female gametophyte 

 commences with the preparations for the first division in the mega- 

 spore mother-cell. As regards this preparatory stage, I find that 

 Ruppia maritima does not deviate essentially from R. rostellata, 



