240 FIRST FORMS OF VEGETATION. 
decaying substances, and excluded from air and 
light. And this opinion seems to be strengthened 
by the fact so well known to botanists, that the 
permanent organization of the lowest plants is 
very frequently only the temporary or transi- 
tional condition of higher, and that so close is the 
resemblance between them that without due care 
in watching the progress of their development, 
they may easily be set down as distinct species. 
To this theory of development, however, plausible 
though it looks, I do not subscribe. Some of 
these productions may not be autonomous, some 
may seem to pass into each other by intermediate 
forms, and may.bear a close resemblance to the 
primordial stages of plants belonging to other 
tribes; but still there are real species among 
these lower genera—species which are permanent 
and do not undergo any further transformation, 
for in the circumstances in which they are found 
they can exist and multiply and perfect their 
fructification independently. Few objects are 
more beautiful and interesting under the micro- 
scope than some of these obscure bodies, and 
their study is absolutely necessary to the physio- 
logist, if he wishes to obtain a clear insight into 
the real character and phenomena of growth and 
reproduction in the higher tribes of plants, and 
especially the changes which take place during 
