6 FIRST FORMS OF VEGETATION. 
place from the various terminal points ; and hence 
they are called acrogens and thallogens, to dis- 
tinguish them from monocotyledonous and dicoty- 
ledonous plants. Popularly, they are known as 
mosses, lichens, alge, and fungi. They open up a 
vast field of physiological research. They con- 
stitute a microcosm, an dmperium in imperio,a 
strange minute world underlying this great world 
of sense and sight, which, though unseen and un- 
heeded by man, is yet ever in full and active 
operation around us. It is pleasant to turn aside 
for a while from the busy human world, with its 
ceaseless anxieties, sorrows, and labours, to avert 
our gaze from the splendours of forest and garden, 
from the visible display of green foliage and 
rainbow-coloured blossoms around us, and con- 
template the silent and wonderful economy of that 
other world of minute or invisible vegetation with 
which we are so mysteriously related, though we 
know it not. There is something exceedingly 
interesting in tracing Nature to her ultimate and 
simplest forms. The mind of man has a natural 
craving for the infinite. It delights to speculate 
either on the vast or the minute ; and we are not 
surprised at the paradoxical remark of Linnzus, 
that Nature appeared to him greatest in her least 
productions. 
These plants once occupied the foremost position 
