BACTERIA. FUNGI. 161 
cover both fresh and salt-water plants. In still inlets of the sea it is not rare to see 
the larger sea-wracks with smaller specimens clinging to them, whilst Floridex are 
fastened to the latter, and minute siliceous-coated diatoms to the Floridex. Even 
in fresh water, eg. in cold and rapid mountain streams, we find little tufts of 
Chantransia or Batrachospermum developed as epiphytes upon the black-green 
filaments of Lemanea, and on the former, again, Diatomacee. One of these 
Diatomacex, which, from its resemblance to a scale insect, has received the name of 
Cocconeis Pediculus, is especially conspicuous, and is often found by the score upon 
the green filaments of Alg®. Such a connection does, no doubt, suggest the idea 
that the Cocconeis drains the green algal cells of nutriment; nevertheless, such an 
assumption is not well founded, and if alge, beset by Cocconeis, derive injury at all 
from their presence, it is chiefly owing to a restriction of their absorption of 
nutrient substances from the surrounding water and to interference with their 
respiration. 
The distinctive property of true parasites does not lie, therefore, in the habit of 
growing upon other plants and animals, or even in the fact of killing their living 
supports, but resides exclusively in the withdrawal of nutrient substances from the 
living vegetable or animal bodies which they invest. 
The plants and animals attacked and drained of their juices by parasites are 
called hosts. 
From the point of view of food absorption, true parasites may be classified in 
three groups. The first group includes generally all microscopic forms which live 
in the interior of human beings and animals, chiefly in the blood; the second 
comprehends fungi possessing mycelia, which have the power of withdrawing by 
the entire surface of their filamentous cells, or by clavate outgrowths of the same, 
nutritive material from the tissues of the host invaded by them; and the 
third group comprises flowering plants wherein the seedling, upon emerging from 
the seed, penetrates into the host, by means of suction-roots or some other part 
which subserves the function of a suction-root, so as to absorb juices from the 
host. 
BACTERIA. FUNGL 
In treating of parasites of the first group, we must, in the first place, refer to 
several of the unwelcome visitors known by the name of Bacteria. They appear 
to be invariably unicellular, sometimes spherical, sometimes shortly cylindrical or 
rod-shaped; some are straight, and others curved in arcs or spirals; a few are non- 
motile, whilst some are actively motile. The largest forms have a diameter of 
+45 inm.; the smallest do not measure more than 345 mm., and are reckoned 
amongst the minutest organisms hitherto revealed by the aid of the best micro- 
scopes. In liquids of suitable chemical composition and temperature, they multiply 
with extraordinary rapidity, reproduction being effected by division. The rod- 
shaped cells elongate somewhat and divide into two equal halves, each half, when 
grown to a certain size, divides once more into two, and so on without limit. 
VoL. I. 
