18 IOWA STUDIES IN NATURAL HISTORY 
out attachment and are held in place by the pressure of sur- 
rounding parts,—the placenta, ovary wall and adjacent ovules, 
—and each is nourished directly by means of its micropylar 
absorbing organ. 
13. Their unusual behavior in Utricularia and similar forms 
suggests that the female gametophyte and endosperm, if given 
favorable opportunity, may assume more marked development 
than is typically displayed. 
14. It seems probable that the constaney of events within 
the ovule of the Angiosperm is correlated with its structure and 
the type of siphonogamy found in this group. The gamet- 
ophytes must follow a precise program and _ post-fertilization 
activities are under ordinary conditions largely under the con- 
trol of the ovule. 
BIBLIOGRAPHY 
1. Balicka-[wanowska.—Contribution a l’etude du sac embryonnaire chez 
certaines Gamopetales.—Flora 86: 47-71. 1899. 
2. Billings, F. H.—Beitrige zur Kenntniss der Samenentwickelung.— 
Flora 88: Heft 3, 1901. 
3. Billings, F. H.—The Nutrition of the Embryo Sac and Embryo in 
Certain Labiatae—The Kansas University Science Bulletin, 5: 
67-83. 1909. 
4, Chamberlain, C. J—Embryo-Sae of Aster novae-angliae—Bot. Gaz. 
20: 205-212. 1895. 
5. Kamienski, F.—Vergleichende Untersuchungen iiber die Entwickel- 
ungsgeschichte der Utricularien.—Bot. Zeit. 35: 761-775. 1877. 
6. Lang, F. X.—Untersuchungen tiber Morphologie, Anatomie und Sam- 
enentwickelung von Polypompholyx und Byblis gigantea.—Flora 88: 
149-206. 1901. 
7. Merz, M.—Untersuchungen iiber die Samenentwickelung der Utricula- 
rien.— Flora 84: 69-87. 1897. 
8. Wylie, R. B—The morphology of Elodea canadensis.—Bot. Gaz. 37: 
1-22. 1904. 
