176 MORPHOLOGY OF ANGIOSPERMS ' 



pylar chamber. In Potamogeton (Holferty 44 ) the endosperm 

 is developed only as a parietal layer of free nuclei; but all of 

 these seem to have come from the micropylar endosperm-cell 

 of the first division, the lower one becoming very large but not 

 dividing, a tendency similar to that in Sagittaria and Limno- 

 charis, but without the formation of a transverse wall in the sac. 



Among the Dicotyledons instances of a chambered embryo- 

 sac are numerous. Hofmeister 1 has given a long list of them, 

 and these, with others added since, are approximately as follows: 

 Among the Archichlamydeae they are the Saururaceae, Loran- 

 thaceae, Balanophoraceae, Santalaceae, Aristolochiaceae, Nym- 

 phaeaceae, Ceratophyllaceae, Loasaceae, a list composed in the 

 main of primitive or saprophytic and parasitic forms. In fact, 

 the chambered sac is distinctly lacking in the more important 

 and characteristic groups of the Archichlamydeae. Among the 

 Sympetalae, chambered sacs occur in the Pyrolaceae, Mono- 

 tropaceae, Vacciniaceae, Hydrophyllaceae (Nemophila), Sola- 

 naceae, Verbenaceae, Selaginaceae, Labiatae, Scrophulariaceae, 

 Orobanchaceae, Bignoniaceae, Pedaliaceae, Acanthaceae, Plan- 

 taginaceae, and Campanulaceae. Although most largely repre- 

 sented among Sympetalae, it will be noted that chambered 

 sacs occur chiefly in saprophytic or parasitic forms, and among 

 the Personales. The phenomenon seems thus to be associated 

 with peculiar conditions of nutrition or a certain configuration 

 of the embryo-sac. 



In the case of two-chambered sacs among Dicotyledons, it 

 does not seem to be common for endosperm to form in both 

 chambers, although this is reported to be the case in Balano- 

 phoraceae, Aristolochiaceae, Pyrolaceae, and Monotropaceae. 

 In the majority of cases the endosperm develops only in the 

 micropylar chamber, in connection with the embryo, as in Sau- 

 ruraceae, Viscum (Loranthaceae), Santalaceae, Xymphaeaceae, 

 Globularia (Selaginaceae), Scrophulariaceae, and Orobancha- 

 ceae. In Saururus (Johnson 34 ) the embryo-sac is flask-shaped, 

 the wall cutting off the neck from the large venter, and the en- 

 dosperm developing only in the former. In Nymphaea and 

 Nuphar (Cook 52 ) the endosperm develops only in the micro- 

 pylar chamber, while the antipodal chamber extends as an haus- 

 torial tube to the chalazal extremity of the ovule. It is of interest 

 to note that until Cook's work the endosperm of these genera was 



