b Colorado Experiment Station 
the material upon which they are growing. Under the high pow¬ 
ers of the microscope these delicate filaments are seen to be thin- 
walled tubes which branch and unite to form an intricate network 
somewhat like the root system of a flowering plant. This network 
of minute tubular threads, known as mycelium, grows rapidly 
under proper conditions of moisture and heat and dissolves and 
absorbs the nutritive substances in the material upon which it 
grows. If this happens to be a mass of fallen leaves, a pile of ma¬ 
nure or a piece of wood, these materials soon show the signs of 
decay. Most fungi require an abundance of moisture to enable 
them to grow. For this reason, the mushroom crop is especially 
abundant during or following a period of wet weather and it is a 
matter of common knowledge that vegetable matter will not decay 
as long as it is kept dry. 
After a fungus has grown in its vegetative stage until it has 
accumulated a supply of reserve food material and has formed a 
well developed mycelial system, it may begin to produce its fruiting 
stage in the form of the mature mushroom or toadstool. A great 
No. 2. Root-like strands of mycelium of the common cultivated 
mushroom giving rise to the button stage of the fungus. This shows how 
the little mushrooms are formed in the mushroom bed. 
many of the little threads of mycelium may unite to form root-like 
strands which in turn give rise to small globular bodies, the future 
mushrooms. This process usually takes place a little below the 
