350 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



(p. 348), an outgrowth which partly and later entirely encir- 

 cles it. This is the plumule-sheath. Subsequently a leaf, 

 the first one, appears on the side of the stem-apex opposite 

 the cotyledon, which agrees with the position of the first 

 leaf in Hordeum (Lermer and Holzner, 1888). The plumule 

 and first leaf thus appear precisely as the leaves in the 

 mature plant, alternating on the stem. 



The homologies of the scutellum, epiblast, and plumule- 

 sheath have been abundantly discussed by many writers 

 (see Introduction), and will only be touched upon in this 

 paper. The scutellum is generally regarded as the cotyle- 

 don. Some authors (1) believe the epiblast to be part of 

 the cotyledon, (2) others that it is simply a projection of 

 the nature of a trichome from the hypocotyl, and (3) 

 still others as a second rudimentary cotyledon. The 

 plumule-sheath has been explained in various ways : (1) 

 it is looked upon as an outgrowth of the hypocotyledonary 

 internode, (2) it is regarded as a third leaf alternating with 

 the epiblast, and (3) finally as a ligule-like growth proceed- 

 ing from the scutellum. My observations on the embryo of 

 Avena lead me to agree with Kennedy (1. c.) in his inter- 

 pretation of the homologies of the epiblast and of the 

 plumule-sheath. That is, the epiblast can probably be con- 

 sidered to be a second cotyledon, although it is not homol- 

 ogous to the true cotyledon, and the plumule-sheath may 

 be regarded to be a ligule-like growth proceeding from the 

 base of the cotyledon, forming an integral part of it, and to 

 be homologous to the ligule of the grass blade. 



While the plumule and plumule-sheath are forming and 

 about the time of the growth in the region of the radicle 

 (referred to as the third period of growth), the cotyledon 

 begins to increase in length and in breadth to form the 

 scutellum of the mature embryo. An examination of the 

 epidermis on the side of the cotyledon next to the endo- 

 sperm shows that the palisade-like cells, which are charac- 

 teristic of the dermatogen of the scutellum in grasses, are 

 already formed. These cells in Hordeum (Lermer and 

 Holzner, 1888) exude an enzyme which dissolves the 

 starch and proteids of the endosperm and renders them 



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