286 MINNESOTA BOTANICAL STUDIES. 



in figs. 58 and 59. The tissues of the petiole are firm, while the 

 portion within the seed is fleshy. The cells of the region which 

 comes in contact with the tissue of the gametophyte are densely 

 packed with starch {fig. jo). The rest have fluid contents. 

 Stomata occur on both surfaces of the cotyledon. 



Summary. 

 The essential features of the embryogeny of Ginkgo can be 

 summarized as follows. 



1. By free-cell-formation, following free-nuclear-division, a 

 spherical protocorm is organized which completely fills the 

 venter of the archegonium. 



2. The basal cells of the protocorm, through continued activ- 

 ity, pass over into the blastema or metacormal bud. 



3. The menstems of the stem and root are localized out of 

 the one general meristem of the blastema. 



4. Cotyledons and leaves arise as exogenous outgrowths 

 upon the growing-point of the stem and are here morphologic- 

 ally homologous structures. 



5. Cases are infrequently met with, where two embryos from 

 different oosperms have developed to maturity in the same seed. 



6. Polyembryony occurs, occasionally, through the produc- 

 tion of two blastemata by one protocorm. 



Bibliography. 

 Cook, Mel T. 1902. Polyembryony in Ginkgo. Bot. Gazette, 34 : 



64-65. 

 Cook, Mel T. 1903. Polyembryony in Ginkgo. Bot. Gazette, 36: 



142. 

 Coulter, J. M., and Chamberlain, C. J. 1901. Morphology of 



Spermatophytes. Part 1. Gymnosperms. 

 Dangeard, P. A. '90. Le mode d'union de la tige et de la racine 



chez les Gymnosperms. Comptes Rendus, IIO: 253-254. 

 Endlicher, S. '47. Synopsis Coniferarum. 

 Fujii, K. '9S. Has the spermatozoid of Ginkgo a tail or not ? Bot. 



Mag. Tokyo, 12 ■ 2S7-290. 

 Fujii, K. '99. On the Morphology of the spermatozoid of Ginkgo 



biloba. Bot. Mag. Tokyo, 13: 260-266. 

 Hirase, S. '95. Etudes sur la fecondation et l'embryogenie du 



Ginkgo biloba. Journ. Coll. Sci. Imp. Univ. Tokyo, 8: 307-322. 

 Hirase. S. '96. On the spermatozoid of Ginkgo biloba. Bot. Mag. 



Tokyo, 10: 325—328. 



