36 EVOLUTION OF PLANTS 
of disease germs, nearly all of which are bacteria. The 
great importance of these minute organisms in the 
economy of nature is at once evident when we reflect 
that, without their assistance, the decomposition of dead 
organic matter would practically cease, and it would 
remain inert and useless as food for the higher plants. 
The presence of bacteria in the soil is of the greatest 
importance, as it is through their agency that the nitro- 
gen compounds are put in such form that they can be 
absorbed by the roots of the higher plants. 
While the position of the bacteria is unquestionably 
very low in the scale, their relation to the higher plants 
is somewhat problematical. The presence of cilia has 
suggested a possible connection with the flagellate 
infusorians. Related to them is a peculiar group of 
simple, green plants known variously as “ Cyanophycex”’ 
— Blue-green Alge—or “Schizophycee ” — Fission 
Alge. Like the bacteria they multiply ordinarily by 
simple, transverse fission, but may also produce resting- 
spores. Being provided with chlorophyll, however, 
they are to some extent independent, but they often 
occur in such positions as to indicate a partial depend- 
ence on other plants for food. Some occur regularly 
within the bodies of higher plants, and are probably 
parasitic to a limited extent. More commonly they live 
free upon damp earth, or in stagnant water (Fig. 4, 
A, B, C). 
Like the bacteria, the cell-structure is very simple, 
and it is doubtful whether a perfectly organized nucleus 
is ever present, although a central structure of doubtful 
nature has been considered by some botanists to be a 
genuine nucleus. They resemble the bacteria, also, in 
