the Embryo and Seedling in the Gramineae. 171 
of the plumule is in a position favourable for the cauline roots it throws out. 
In a seedling produced from a grain which had been planted with the 
glumes pointing upwards, the mesocotyl ceased to grow when it had just 
overtopped them. Two foliage leaves were expanded at that time, and 
a third was appearing from the sheath of the second. The upper limit of 
the mesocotyl was clearly defined in this seedling by the sudden increase 
in diameter of the epicotyledonary axis with its sheathing leaves, and also 
by the appearance of rudimentary cauline roots at the first node (Text- 
fig. 15). By this time the food reserves of the endosperm are exhausted 
Text-figs. 12-14. Avena sativa, L. 12. Whole seedling, life-size. Part of grain is removed, 
exposing half scutellum. 13. All grain removed. Scutellum and adjacent parts from back, x 4. 
14. Scutellum from front, showing ventral scale ( v.s .). The scar pi. shows place whence plumule 
has been removed, x 4. 
Text-fig. 15. Avena sativa , L. From much older seedling, which showed three leaves. Grain 
with median region of axis attached. The mesocotyl is surrounded by the husks of the grain. 
Nodal roots show as rudiments, x 3. 
and the scutellum is functionless. The young plant will depend in the 
future on its green leaves only for supplies of food, and these leaves are 
developing a root-system of their own. The older root-system perishes by 
degrees ; the cauline roots first, and then the primary root. In time all the 
lower members of the seedling—scutellum, mesocotyl, primary and insertion 
roots—having served their purpose, will disappear and leave the mature plant 
rooted at the first node. 
We are concerned here, however, with the structure of the seedling in 
its early stages, before the epicotyledonary members have become functional. 
