FUNGI. 13 



fruit trees, etc., but such attacks are uncommon; most of the 

 species are simple saprophytes, and with this brief mention of the 

 fact, we must pass to the second group, the Ascomycetes. In this 

 group are found very many of our most pernicious parasitic fungi. 

 Their parasitic effects are readily seen when a potato vine blights, 

 or the familiar velvety brown blotches called " scab" appear upon 

 the leaves and fruit of our apple trees. But the fungi themselves are 

 very minute ; -they are never so conspicuous as the larger forms of 

 Basidiomycetes, and hence they frequently escape notice, the 

 diseased condition which they cause being usually attributed to 

 some more visible agency. 



Perhaps the most intelligible method of getting at the character- 

 istic points of the Ascomycetes, will be to follow out the life- 

 history of some common form. You are all familiar with a white 

 or bluish-green mold which readily develops upon old cheese, 

 bread, leather, and in fact almost any organic substance if kept in 

 a damp place. If a portion of this mold be placed first in a drop 

 of alcohol and then in water, and examined under the microscope, 

 the hypha? will be seen extending in all directions and forming an 

 entangled mycelium. Here and there the mycelium w^ill be seen 

 to have produced delicate branches rising from the substratum into 

 the air. The tip of each of these branches is swollen into a 

 globular vesicle, on the surface of which are borne chains of 

 spores, which seen separately appear colorless and transparent, 

 but in the mass are greenish or bluish in color. If one of these 

 spores, while still living, falls upon a substance suitable to its 

 growth, it soon puts out a delicate hypha, which rapidly elongates, 

 and branches profusely ; these branches interlace and finally we 

 have a typical mycelium, from which in due course arise the spore- 

 bearing threads. So far the process of reproduction is simple 

 enough. But the mycelium arising from the spore may produce 

 reproductive bodies of another form. The tip of one of the 

 hypha^ may become coiled in corkscrew fashion and, after being 

 fertilized in a peculiar manner by a branch which grows up from 

 below, it becomes enclosed in a network of hyphal branches ; the 

 latter become denser and externally hardened, and finally form 

 small yellow knots, within which the spiral is completely enclosed. 

 On breaking open one .of these knots, which are plainly visible to 

 the naked eye, being about half the size of a pin-head, the 

 microscope shows that from the swollen cells of the original spiral, 

 little spherical or club-shaped sacs have arisen, each containing 



