78 ELEMENTS OF PLANT ANATOMY..- 
branches of the cormophytes. The apical cell of this plant is 
cylindrical, terminating in a convex surface, and the axis is 
increased in length by segments cut off from this cell by walls 
at right angles to the main axis of growth. These segments 
grow to a certain length and then rapidly divide by walls in 
three directions, thus forming a cell body whose terminal por- 
tion remains as a single row of cells. Other changes occur by 
which the form of the whole plant is greatly modified, but it is 
not necessary to continue the description further. 
The indication of division into systems is stronger in the 
aloae than in the fungi ; especially is this true of the outer 
layers of cells, which in the higher forms closely resemble the 
epidermis of phanerogams. ‘The cell contents are quite differ- 
ent from those of fungous cells ; a nucleus is generally present, 
and chlorophyll either in form of grains or pecularly shaped 
bands and stars. The color is often hidden by other coloring 
matter, but the latter may be extracted by artificial means and 
the pure chlorophyll left behind. 
3. Lichens. 
It is now generally admitted that the plants of this group 
consist of a combination of fungi and algae, whose relation to 
each other is that of parasite and host. Accepting this"theory, 
we cannot look for one-celled forms, nor find it possible to go 
back to the beginning of growth as in case of other plants. 
Experiments in cultivating lichens have partially succeeded, 
but we are still ignorant of the exact processes or first stages of 
growth which take place in nature. In the grown plant are 
found two distinct portions, — the one of fungous, the other of 
alga tissue. Generally there are two kinds of layers of fungous 
tissue, corresponding to pith and rind of higher plants, then 
another layer of algae, the separate elements of which were 
named gonidia when first discovered. They still retain this 
