THE PARTS OF THE SEEDLING. 15 
called water-hyacinth! that which occupies the place of an 
ordinary root-cap is a long sheath, which may be pulled off 
entire; its large size is possibly due to the fact that it is not 
worn away by friction against the soil. 
19. The Young Stem.—The caulicle, or portion of the 
stem which lies below the cotyledons, is the earliest-formed 
portion of the stem. Sometimes 
this lengthens but little; often, 
however, as the student knows 
from his own observations, the 
caulicle lengthens enough to 
raise the cotyledons well above 
ground, as in Fig. 5. 
The later portions of the stem 
are considered to be divided into 
successive nodes, places at which 
a leaf (or a scale which repre- 
sents a leaf) appears, and inter- 
nodes, portions between the 
leaves. 
The student should watch the 
growth of a seedling bean or pea 
and ascertain by actual measure- 
ments whether the internodes 
lengthen after they have once 
been formed, and if so, for how 
long a time the increase con- 
tinues. Fic. 5.—I1,a seedling maple, natural 
. size ; c, cotyledons; d, plumule; o; 
The rate of growth may readily be level of the ground ; II, part of root 
measured by means of a simple piece of the same, magnified six times, 
of apparatus, shown in Fig. 4. This showing root-hairs. 
consists of a pointer Z supported by 
an upright stand, moving over a graduated arc, and with a grooved 
1A plant somewhat common in greenhouses, allied to the ordinary pickerel weed 
of the streams and ponds of New England. 
