12S BOTANT. 



to form a mycelium: that is always the result of the growth 

 of the spores from the spore-cases. 



2685. The Insect-fungi {EntomopMhorecB) are well rep- 

 resented by the Fly-fungus (Empusa muscae) which in 

 the autumn is so destructive to house-flies. It consists of 

 small tubular cells which grow in the moist tissues of the 

 fly, and at last pierce the skin, producing minute terminal 

 spores, which give the fly a powdery appearance. These 

 spores (called, also, conidia) may be seen as a whitish halo 

 surrounding the spot to which the fly (now dead) has at- 

 tached itself. Resting-spores have been observed in some 

 species. They are round and thick-walled. 



Protctkal Studies. — {a) Collect a quantity of Pond Scum and other 

 aquatic vegetation, and preserve in a dish of water. Mount portions 

 of this material and search for desmids, using a ^-inch objective. 

 Two-lobed or star-shaped desmids of a bright-green color may fre- 

 quently be found. A large lunate desmid (Oloslerium, Fig. 54) is 

 often still more common. In the latter the clear protoplasm at each 

 end is always streaming rapidly. 



(J) Collect a little of the brownish-yellow scum which in early 

 spring gathers on the top of the water of brooks, ditches, and pools. 

 Mount in water and examine with a high power. Hundreds of dia- 

 toms may be seen moving rapidly across the field in every direction. 

 In any such preparation many species of various shapes will be 

 found. The prevailing form, however, is generally elongated and 

 somewhat diamond-shaped. 



(c) Study in like manner the slimy coating upon dead leaves and 

 twigs in water in the summer for diatoms. On some of these, very 

 fine markings may be found. 



(d) Collect a quantity of bright-green Poud Scum which always 

 abounds in shallow ponds and pools, and preserve in a dish of water. 

 Collect, also, some of the same which has begun to turn yellow and 

 brown. Upon mounting a bit of the first in water and examining 

 with a high power, it will be found to consist of threads of cylindri- 

 cal cells, each containing one or more spiral chlorophyll-bands (Spi- 

 rogyra. Pig. 56) or star-shaped chlorophyll-bodies (Zygnema). Upo^ 



