THE TWO MAJOR TYPES OF ANGIOSPERM EMBRYOS 359 



sionally among the dicotyledons in taxa sometimes called "pseudomono- 

 cotyledons" and "aberrant dicotyledons" — Trapa, Cyclamen, Abronia, 

 Conjdalis, Dicentra, Erigenia, Pinguicula, Caruni, Peperomm, Claytonia, 

 Ranunculus Ficaria (the most thoroughly studied taxon), the Nym- 

 phaeaceae. In Trapa, Eranthls, and Mammillaria, one cotyledon is 

 smaller than the other. Cyclamen — long known for its unusual germina- 

 tion — has one well-developed cotyledon and a second one represented 

 by a small vestige; both cotyledons remain within the seed — the well- 

 developed one serves as an absorbing organ; the embryo and germina- 

 tion are essentially those of a monocotyledon. CorydaUs cava and C. 

 ochroleuca differ from other species of the genus in their solitary cotyle- 

 don; a second cotyledon is represented by a "hump" opposite the well- 

 developed one. In Cloytonia virginica, one cotyledon is very small, and 

 the embryo closely resembles that of the aberrant embryos of the 

 Dioscoreaceae and Commelinaceae which have a second cotyledon. 

 Species of Pinguicula show stages in the abortion of one cotyledon. 

 P. vulgaris and P. alpina have only one cotyledon; P. leptoceras has 

 one normal and one in which development ceases at various stages. 

 The Umbelliferae perhaps provide, within one family, the most ex- 

 amples of suppression of the second cotyledon. Eight genera have 

 species with one cotyledon. Bunium and Scaligera have some species 

 with two, others with one cotyledon. 



The embryo of Ranunculus Ficaria has been cited in support both of 

 the view that, in the monocotyledons, one cotyledon has been lost, and 

 also of the view that the one cotyledon of some embryos represents 

 two fused cotyledons. In this species, most embryos have two cotyledon 

 primordia, one of which aborts after forming a flattened appendage, 

 and the embryo much resembles that of the monocotyledons. A few 

 embryos in this species have fairly normal pairs of cotyledons. The 

 structure of the two forms of embryo in this species was seen as evi- 

 dence to support the view that the solitary cotyledon represents a union 

 of two. The fusion of the cotyledonary petioles to form a unit structure, 

 extending, in some individuals, to the cotyledon, which then is bilobed, 

 was considered additional evidence. In refuting this theory, it was 

 pointed out that each lobe is itself bilobed and that cotyledons of 

 many angiosperms, even those of some monocotyledons, are bilobed. 

 Sheathing cotyledonary bases are frequent in all the angiosperms, 

 especially in geophilous taxa — Eranthls, Podophyllum. Fusion of the 

 two cotyledons may extend so far into the cotyledons that the embryo 

 has been described as having only one, bilobed cotyledon. 



The existence of unusual cotyledonary structure in the water lilies 

 has been much discussed. Neliimbo was described as having only one 

 cotyledon. The genus was termed monocotyledonous, and the sugges- 



