2 CIRCULAR 143, U. S. DEPARTMENT OF AGRICULTURE 
FUNGI IN GENERAL 
The plants known as fungi comprise a very large group and exhibit 
great variation in form, size, color, and habit. The one important 
character common to all fungi is the absence of the green coloring 
matter known as chlorophyll, by means of which, through the aid 
of sunshine, higher plants are able to manufacture their own food. 
The structure of fungi is very simple; that is, it has not become 
highly differentiated or specialized as in flowering plants. Fungi 
have very simple physiological processes and are incapable of manu- 
facturing their own food, but live as parasites or saprophytes, appro- 
priating food already prepared by higher forms of plants. Occur- 
ring as parasites, they are responsible for extensive losses to agricul- 
tural crops and produce blights, rots, unsightly growths, rusts and 
smuts of grain, and diseases of ornamental and forest trees. In- 
juries from fungi are not confined entirely to plants but are some- 
times the cause of disease in man and in animals. 
One of the great advantages pertaining to the study of fungi as 
a hobby or diversion is that their occurrence, unlike that of many 
other plants, is not hmited to a short calendar period but extends 
practically throughout the entire year. The appearance and abun- 
dance of mushrooms are subject to great variation, largely depend- 
ing on weather conditions. This variation is influenced not only 
by the weather of the current season but also by that of the preced- 
ing year. Two important factors in the growth of fungi are heat 
and moisture. If the preceding year has been excessively dry, the 
underground or vegetative part of the fungus, known as the myce- 
lium, and the minute reproductive bodies, known as spores, may 
have dried up or at least suffered a loss of vitality that would retard 
or discourage the appearance of many fungi the following season. 
On the contrary, a hot but wet season is highly conducive to the 
abundant production of mushrooms. The almost phenomenal ap- 
pearance of fungous growths under such conditions has led to the 
stories of the seemingly miraculous appearance of mushrooms over- 
night. That fungi develop very rapidly is partly explained by the 
fact that much of the tissue is formed before the fungus breaks 
through the surface of the soil. In addition, fungous tissue is espe- 
cially adapted to the rapid absorption of water, and as a result the 
growing plant expands very rapidly. 
As already mentioned, fungi exhibit a remarkable diversity in size, 
form, and color. They vary from microscopic organisms, many of 
which cause plant diseases, to the large woody growths present on 
many injured or dying forest trees. In form or structure they range 
from very simple 1-celled structures to the fantastic complicated 
stinkhorn fungi. (Fig. 45.) The greatest variation in color may 
also be observed. In some species the colors are often very unob- 
trusive and quiet, while in other species they are striking in their 
diversity and brilliancy. 
One very striking phenomenon exhibited by certain fungi is lumi- 
nosity or phosphorescence. This character, while confined to a com- 
paratively few fungi, is so striking or ghostlike as to have furnished 
material for fairy stories and among the natives of certain countries 
the basis for‘many superstitions. An Australian species is recorded 
