CLASSIFICATION. 19 
into long, straight, wavy, or spiral filaments. These filaments may 
break up into cocci-like reproductive elements—‘‘ arthrospores.” 
LEPTOTRICHE-E (Zopf).—The vegetative cells present rod-shaped 
and spiral forms, and grow out into straight, wavy, or spiral fila- 
ments ; these may show a difference between the two extremities, 
of base and apex. Cocci-like reproductive bodies are formed by seg- 
mentation of the rod-shaped elements in these filaments. In some 
of the species the segments are enclosed in a common sheath. Sub- 
genera: LEPTOTHRIX, BEGGIATOA, CRENOTHRIX, PHRAGMIDIO- 
THRIX (for generic characters see page 12). 
CLADOTRICHEH (Zopf).—The vegetative cells are rod-shaped 
or spiral, and grow out into straight or spiral filaments, which may 
present pseudo-ramifications. Asingle genus, CLADOTHRIX (see 
page 12). 
The various methods of classification heretofore referred to must 
all be considered provisional and unsatisfactory from a scientific 
point of view. Thus Hueppe says: “The existence of rigid form 
species, which not only the earlier observers, but even Cohn, Schroter, 
and Koch assumed, can be upheld no longer. The adaptability of 
bacterial forms to changing conditions of nutrition is not so bound- 
less as Naegeli and Billroth supposed, but it is considerably greater 
than was once held to be compatible with the conception of the ex- 
istence of constant species.” 
A. Fischer has attempted to make use of the presence, number, 
and mode of attachment of flagella as a means of classification. No 
doubt this character and the presence or absence of spores should re- 
ceive consideration in any attempt at a scientific classification of the 
bacteria. 
