DISEASES OF CULTIVATED PLANTS 323 
PARTICULAR FACTS ABOUT PARASITIC FUNGI 
Like the bread mold, or the other fungi just mentioned, parasitic 
fungi consist of a growth of threads or hyphae (singular, hypha) 
which-do the necessary work of getting food for the parasite; these 
also in due time give out certain branches destined to bear spores, 
somewhat after the manner that the pear tree has flower clusters, 
or the wheat plant forms its dense spike of bloom, both of which are 
especially designed to produce seeds from which wheat plant and 
pear tree may inturn be grown. The essential parts of a parasitic 
fungus are these threads, or hyphae, and the spores produced by 
them. ‘The hyphae of the fungus taken collectively are called the 
mycelium, which consists of threads that produce no spores (sterile 
hyphae) and of those destined for spore production (fertile hyphae. 
(Figure 7). Itis to the food getting qualities of the hyphae that the 
fungus owes its continual existence, and they in turn arise from a 
spore or directly by the growth of some fragment of fungus-thread, 
as the Carolina poplar may be grown fromacutting. Yet, while all 
parasitic fungi are made up of these few parts, the differences in 
form and apparent structure among the several groups are very 
marked; differences exist as to the thickness of the hyphae whether 
or not the threads are divided into separate cells by divisions like 
those at the joints of a bamboo rod, as wellas in the manner of spore 
formation and in the size, color, form markings and structure of the 
spores themselves. It is almost hopeless to undertake to illustrate 
types of spore production and spore forms, since these are so varied 
and may differ so much at different stages of the development ofa 
single given species of fungus, yet we may cite a few examples: 
Fig.9. Showing the common rust of oats and rye. At Aasmall fragment of rye leaf with 
several orange-red, rust sori breaking through the epidermis; these are of the earlier summer 
spores (Uredo) or red rust of popular speech. At B asmall fragment of a rye leaf with several 
black, rust sori, elongated in form, breaking through the external covering; these are of the later 
summer or winter spores (Z¢lewtospores), AandCslightly magnified. At C section through 
thg uredosorus of 4; on the slender stalks (basidia) the rough one-celled uredo spores, and 
between them a young, two-celled teleutospore, which later alone form the sorus. ¢, ¢; epi- 
dermal cells; /, 2, cells of the leaf interior through which runs the mycelium of the fungus. At 
D a teleutospore from the black sorus of B; this is divided by a septum into two cells. Similar 
uredospores are found in most rusts; similar teleutospores occur in corn rust, wheat rust, etc., 
and in the spores of the cedar apple fungus. C and D considerably magnified. (After Zopf, 
