the Embryo and Seedling in the Grammeae. 
163 
-scutellum 
from other Monocotyledons for comparison. But before describing our own 
researches, we will outline the points in dispute. 
The members of doubtful homology are shown in the diagram of 
a seedling A vena (Text-fig. 2). The same parts are present in the embryo 
with the exception of the 
mesocotyl. This appears first 
on the elongation of the axis 
during germination (compare 
Text-figs. 1 and 2). 
In the young seedling of 
a hypogeal Monocotyledon, 
two members are distinguished 
externally : the cotyledon, and 
the main descending axis. The 
plumular bud is present, but 
is commonly concealed within 
the expanded base of the coty¬ 
ledon. This expanded base, 
with or without an appendage, 
forms the sheath , which pro¬ 
tects the plumule during ger¬ 
mination. The apex of the 
hypogeal cotyledon becomes 
the sucker , absorbing food from 
the endosperm. Sucker and 
sheath are usually connected 
by a stalk , which may be very 
short or absent. For instance 
in Tigridia (Text-fig. 8, p. 8) 
the seed appears to cling to the 
sheath, but on removal of the 
seed-coats a short neck is found 
between sheath and sucker. 
The scutellum of Avena 
seems perfectly comparable 
with the sucker of Tigridia for 
example, and the coleoptile re¬ 
sembles such sheaths as those 
of Tigridia , Crocus , Colchicum , and Elettaria. But in Avena and similar 
forms, as in the Zea type also, scutellum and coleoptile are separated from 
each other by the mesocotyl,which is sometimes very long (Text-fig. 18,p. 179). 
If this were not so—that is, if throughout the Gramineae the coleoptile and 
scutellum were inserted on the axis at the same level (as in Hordeum and 
M 2 
Text-fig. 2. Avena sativa, L. Diagram of part 
of very young seedling in median section. 
