280 MINNESOTA BOTANICAL STUDIES. 



and in one such exceptional case three young embryos were 

 found. Of the two embryos often formed in one seed, the 

 more vigorous soon occupies the central, non-resistant tissue of 

 the gametophyte, while the other aborts. In the many seeds 

 examined, only one case has been found {Jig- 29) where two 

 embryos from different oosperms have developed to maturity 

 in the same gametophyte. Several cases, however, have been 

 met with, where two metacorms have resulted through the 

 production of two blastemata by one protocorm. Figs. 36 and 

 37 show two such cases ; while rig. 9 shows an instance where 

 two blastemata have arisen on one protocorm, and then one has 

 aborted. 



6. The Mature Embryo of the Seed. — The single embryo 

 figured and described by Seward and Gowan (1900) was, with- 

 out question, a freak ; for it bears little resemblance to a typical 

 embrvo. The general description of Ginkgo embryos given 

 by Coulter and Chamberlain, as quoted above, was undoubtedly 

 constructed from that of Seward and Gowan ; for they describe 

 the same anomalies as constant characters of the embryo. 



A very good idea of the embryo of the seed can be obtained 

 through an examination of the photographs of Plates XXXIY- 

 XXXVI. Figs. 23 and 25-28 are typical dicotyledonous, and 

 figs. 22 and 30-34 typical tricotyledonous embryos. Figs. 13- 

 17 are sections of a dicotyledonous, and figs. 18 and 19 sections 

 of a tricotyledonous embryo. Occasionally freakish, deformed 

 embryos are met with, but are no more numerous than is usual 

 in other plants. The one portrayed in fig. 35 is the only one 

 among the hundreds examined which approximated the one 

 described by Seward and Gowan ; and the shorter cotyledon of 

 this one was quite entire. The embryo, portrayed in fig. 24, 

 is one of several found showing a condition intermediate 

 between typical dicotyledonous, and tricotyledonous embryos. 

 Ficj. 20 is a section of the same embryo. In this case a third 

 leaf was produced at the base of the plumule on the same level 

 as the cotyledons. It was, however, partially enclosed by the 

 functional cotyledons {Jig- 20), and in length only equalled the 

 plumule. The stele of this embryo was triangularly prismoidal 

 as in the case of typical tricotyledons. Fig. 21 is a section 

 through the cotyledons of an apparenth' dicotyledonous embryo, 

 which was morphologically tricotyledonous ; two cotyledon- 

 primordia having developed conjointly, producing a single 



