THE PLANT BODY. 61 
entiation into members is not so marked as in the higher, 
and in passing downward in the vegetable kingdom groups 
are reached in which it is inappreciable, and finally in 
which it is entirely wanting: such an undifferentiated 
plant-body is called a Thallome, and may properly be re- 
garded as the original form, or prototype. 
117. Thallome.—The simplest thallome is the single cell; 
this, though, generally rounded, is in some cases irregu- 
larly extended into stem-like or leaf-like portions, which 
may be regarded as, to a certain extent, foreshadowings or 
anticipations of the members of the higher plants. Plants 
composed of rows of cells or cell-surfaces frequently show 
no indication whatever of a division into members; but in 
some cases there is a little differentiation, which, though 
not carried far enough to give rise to members, is the same 
in kind. 
118. In the larger seaweeds there is sometimes so much 
of a differentiation that it becomes difficult to say why 
certain parts ought not to be called members. Structures 
of this kind are instructive, as showing that the passage 
from the thallome plant-body to that in which members 
are differentiated is by no means an abrupt or sudden 
one. 
119. Caulome.—By this general name we designate all 
axial members of the plant. In the more obvious cases the 
caulome is the axis which bears leaves (foliage), and in this 
form it constitutes 
(1) The Stem; branches are only stems which originate 
laterally upon other stems. aor 
The other caulome forms are: 
(2) Runners, which are bract-bearing, slender, weak, and 
trailing. 
