104 



MORPHOLOGY OF ANGIOSPERMS 



into the micropyle, as in Hemerocallis, Crocus, Gladiolus, 

 Romulea (Ferraris 120 ), Alchemilla (Murbeck ,J4 ), in which the 

 sac pushes through to the tegumentary tissue closing the micro- 

 pyle, Medicago, Torenia asiatica (Strasburger 5 ), Labiatae, 

 Vaillantia (Lloyd 67 ), Diodia and the Galieae (Lloyd 105 ), and 

 many other forms. In Vaillantia the mother-cell migrates into 

 the micropyle and develops there. 



While ordinarily the embrvo-sac is relatively broad and 

 rounded at its micropylar extremity, this is by no means so 



commonly true of the antipodal 

 end. If the antipodals are ephem- 

 eral, the growth of the antipodal 

 region is frequently checked after 

 the first division of the megaspore 

 nucleus, and through the growth of 

 the rest of the sac it becomes a 

 very small pocket, as in Typha, 

 Potamogeton, Sagittaria, certain 

 Gramineae, Pontederia, Lilium, 

 Oenothera, etc. (Fig. 79). It is 

 generally true that the antipodal 

 region of the sac is narrower than 

 the micropylar, but its growth is 

 not often checked so completely 

 and so early as in the eases cited. 



In other cases, the antipodal 

 region of the sac grows very active- 

 ly, elongating toward the chalazal 

 region and penetrating it more or 

 less deeply, resulting in a very nar- 

 row and elongated sac. Such an 

 antipodal region must be regarded 

 as an haustorium that digests and 

 absorbs its way into the chalazal tis- 

 sue. Illustrations of this are very numerous, as in Gramineae, 

 Tricyrtis ( Ikeda 10c ), Scitamineae, Saururaceae, Loranthaceae, 

 Polygalaceae, Lythraceae, Aceraceae, and most Sympetalae. 

 In penetrating the chalaza the antipodal tip usually remains 

 narrow, but in Saururus (Johnson 87 ), Scitamineae (Hum- 

 phrey 40 ), Cuphea (Guignard 12 ), Campanula (Barnes 18 ), etc., 



Fig. 49. — Saururus cernuus. Longi- 

 tudinal section of embryo-sac; 

 after the first division of the en- 

 dosperm nucleus the micropylar 

 cell has given rise to endosperm 

 tissue, while the other cell has 

 become a large vesicular hausto- 

 rium. — After Johnson.* 



