THALLOPHYTES 
II 
reproduction only by vegetative multiplication, the cell-divisions being 
simple but in remarkably rapid succession. However, in most forms 
there is no chlorophyll, so that bacteria in the main are parasites and 
saprophytes. 
The immense economic importance of bacteria has stimulated their 
investigation to such an extent that bacteriology has become a distinct 
field of research, with its special technique. An outline of plant mor- 
phology can only indicate the existence of this great region of research, 
for to enter it would demand a course in bacteriology; but bacteria are 
plants, and their general place among other plants must be considered. 
Bacteria include the smallest known organisms, cells having been 
measured that are only 0.0005 mm - m diameter. The cells are either 
solitary or they may form 
filaments, as among the 
Cyanophyceae. For general 
purposes, individual cells are 
often referred to three form 
groups : coccus forms, in 
which the cells are spherical; 
bacterium or bacillus forms, 
in which the cells are oblong 
or have the form of short 
rods; and spirillum forms, 
in which the cells are curved 
(figs. 13-20). When these 
various forms of cells enter 
into the structure of fila- 
FIGS. 13-20. Bacteria: 13, coccus form, from 
pus; 14-18, bacillus forms (14-17, hay bacillus); 
14, motile cell; 15, filament of motile cells; 16, non- 
motile cells; 17, cells with "spores"; 1 8, typhoid- 
ments, corresponding varia- fever u ^ m WacUlustypht); , 9 20 spirillum forms; 
r 19, cholera form (Vtbno cholerae); ao, Spirillum 
tions in the form of the undula. After A. FISCHER. 
filaments follow. 
The occurrence of bacteria may be described as almost literally every- 
where: in waters of every depth, in air, in soil, in all organic bodies, 
living or dead, etc. Their resistance to conditions impossible for other 
plants to endure is remarkable a feature suggested by their asso- 
ciates, the Cyanophyceae. Extreme cold, high temperatures, and desic- 
cation that would destroy ordinary plants are successfully withstood 
by bacteria. 
Structure. The structure of the bacterial cell appears to be extremely 
simple ; in fact it may be said to be almost structureless. The proto 
