324 OHIO EXPERIMENT STATION: BULLETIN 214 
Fungus spores may be produced as single spores or in naked 
clusters attached to certain branches. We find this sort in the 
downy mildew of the cucumber and its relatiye the peronospora of 
mustards (Fig. 8); in potato early blight; in fruit rot of plum, cherry, 
peach, etc., and later in the spores of apple scab. ‘They may also be 
found in dense clusters breaking through the skin of the plant like 
the many tubers of a potato breaking through the earth-crust; such 
without further conspicuous covering are found in the rust spots, 
in the anthracnoses and the like. (Figs. 3and 9). These dense clusters 
may arise beneath a special covering resembling nothing so much as 
the traditional beehive, but are usually ejected forcibly from a 
specially provided opening at the top of the cone or half-ball. (Fig. 
10). A yet more interesting class is that in which the spores are 
packed so many to a sac 
(usually eight) and a large 
number of these crowded 
into a ball-like, hollow spore- 
case, such as we find in 
black-Ixnot, strawberry leaf- 
spot, the powdery mildews 
nae A an cam reid ate tet al-pet and in some other instances. 
flexuous mass of spores, ejected from the pycnidium. 4, (Fig. 11). ‘There is yet an- 
section of a pycnidium, seated in the leaf tissues and filled other sort in which the 
with spores. ¢,agroupofthe spores. All highly mag- 
Nified. (After Allescher from Delacroix). Spore sacs are abundant 
near the surface of the dis- 
eased part, as in leaf-curl of the peach, where the maturity of the 
fungus is shown by the change in color of the affected leaf surfaces. 
Other gradations will be found as one proceeds in this study. 
9 
008° 
THE SURVIVAL OF PARASITIC FUNGI 
Further, respecting parasitic fungi we must realize that they 
are all derived by specific processes of reproduction peculiar to the 
fungus in question; in other words spontaneous generation does not 
find support among the students of plant diseases. 
The presence of any given fungus leads us at once toinfer the 
previous existence, somewhere within reach, of a fungus of like 
species from which this one was derived by definite methods of 
reproduction. Likewise, the destructive prevalence of a parasitic 
fungus in any given time and at any given place, assures us of the 
necessary supply of spores to start the trouble again under favorable 
conditions. In fact, all our study leads us to look through mere 
phenomena, mere evidences of disease, to find the specific parasitic 
growth which causes them and the favoring conditions under which 
