DISEASES OF CULTIVATED PLANTS 321 
Herein they are marked off from most groups of plants: the fungi 
must live upon the substance of living or dead plants or animals. If 
they ever possessed the power of utilizing the same foods as most 
other plants, this ability has been lost. Parasitism is usually taken 
to indicate degeneracy in character. One way of regarding the 
fungi is as alge without chlorophyll, to which the latter owe their 
green color. As above stated, the fungi are, in the absence of 
chlorophyll, forced to live upon the dead remains of plants or 
animals, or to prey upon the living organisms. 
CLASSES OF FUNGI 
Such fungias subsist upon living plants or animals are called 
parasitic fungi. A parasite is one who eats at another’s table and 
the adjective ‘‘parasitic” comes from this word, parasite. It is the 
parasitic fungi especially of which we must learn, since this class 
produce diseases when they attack other plants. The plant attacked 
is the “host” plant, 
however unwilling the 
entertainment of the 
sycophant. 
Most fungi are very 
minute in size and 
require the use of a 
microscope to study 
their parts; certain 
ones, however, such as 
the mold upon bread 
or other foods, may be 
seen very easily to 
consist of fine, thread- . 
a . Fig. 6. Mycelium of the common mold (Mxcor Mucedo). 
like g rowths interwov- From the spore lying near the middle of the figure, and strongly 
en toge ther, and __ swollen, one sees the thick threads of the mycelium arise; these 
A < inturn become richly branched. There are nodivisionsin the 
bearing certain round- mycelium. From the level of the mycelium arise three vertical 
ed parts upon erect fertile hypae, 2, 4, ¢, of which @ is still very young and that at 4 
. is already producing a sporangium containing manyspores. All 
branches. Some idea highly magnified. (After Zopf, from Reinke). 
of fungus-structure 
may be obtained by studying these common molds; that ona dis- 
carded melon rind will shows the parts above described, and by the 
use of a microscope we may learn that the rounded, ball-like enlarge- 
ments just mentioned consist chiefly of small bodies that are 
capable of growing into other fungus-threads. (Fig. 6). Such min- 
ute parts capable of germinating and again producing the fungus 
are called spores. Most sporesare very minute and are not heavier 
