CHAPTER IX 
GALLS CAUSED BY FUNGI AND MYCETOZOA 
UNGI are plants without a system of true tissues and 
X without chlorophyll; the tissues are replaced by inter¬ 
twining threads known as “ hyphae.” Oxygen is absorbed, 
and carbon dioxide is given off. The order is a very large 
one, comprising minute species known popularly under such 
terms as rust, smut, mould, and mildew, also the larger 
species, often spoken of as mushrooms and toadstools. The 
majority may be arranged under two headings, saprophytes 
and parasites. There are some intermediate forms. Certain 
saprophytic fungi may become true parasites. Saprophytic 
fungi flourish on dead organic matter, such as rotting wood, 
leaves, etc. Parasitic fungi feed on living organic matter, 
either plant or animal; many that occur on plants give rise 
to gall structures. 
A parasitic fungus lives at the expense of its host as a 
rule, and confers no benefit in return, but many instances 
may be adduced in which a kind of give-and-take arrange¬ 
ment exists between host and parasite; such is known as 
symbiosis or mutualism. It may be seen in all lichens, a 
lichen being a composite plant, made up of a fungus and an 
alga, the latter the host, the former its parasite. 
In some cases symbiosis favours vigorous growth and 
the production of more seeds than in the case of plants not 
affected by the parasitic fungus— e.g ., the hyphae which 
occur in Lolium temulentum and other grasses of the same 
genus. Spherical tumours occur on the root-fibres of 
many leguminous plants— e.g., the Bird’s-foot Trefoil and 
