. Minnesota plant diseases. Plant diseases. 34 Minnesota Plant Diseases. very much lower temperatures. Very many spores of our fungi must be able to endure forty degrees below zero Fahr. to pass the winter. In fact many can undergo still lower temper- atures and survive. Conditions of spore germination. When a spore is placed under proper conditions of moisture, temperature and of other factors, it germinates, i. e., grows out into a fine thread which, if conditions remain favorable, develops directly into the fun- gus mycelium. By far the largest majority of fungus spores are capable of germi
. Minnesota plant diseases. Plant diseases. 34 Minnesota Plant Diseases. very much lower temperatures. Very many spores of our fungi must be able to endure forty degrees below zero Fahr. to pass the winter. In fact many can undergo still lower temper- atures and survive. Conditions of spore germination. When a spore is placed under proper conditions of moisture, temperature and of other factors, it germinates, i. e., grows out into a fine thread which, if conditions remain favorable, develops directly into the fun- gus mycelium. By far the largest majority of fungus spores are capable of germination as soon as they are ripe, provided, ^ of course, that such external conditions as light, moisture, etc., are favorable. Many so-called rest- ing spores are forced to undergo a cer- tain resting period after maturity be- fore they can germi- nate. Such spores are provided with thick coats for pro- tection. This resting period is often connected with the suc- cession of seasons. For instance most of the rust winter spores germinate best in the following spring and cannot be made to germinate before that time. Moreover, they retain but a decreasing vitality as the following summer passes, and are usually incapable of growth in the fall. Such spores are adapted closely to the seasons. Not only resting spores but other non-resting spores may also evince such conditions. Rust summer spores are generally incapable of germination after the summer in which they are formed, though some are probably capable of surviving the winter in vigorous condition. Such adaptations are of course especially bound up in the pe- culiar habits of the Fig. 15.—A caterpillar-fungus (Cordyceps) spore. A germinating spore at different successive stages of several hours apart. The small resulting mycelium is seen below. Highly magnified. By the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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