358 FIRST FORMS OF VEGETATION. 
fers from the two preceding kinds in having its 
spores, instead of being exposed naked to the air 
like them, enclosed in a rounded membranous 
case, bursting irregularly as the spores arrive at 
maturity, which then present themselves like so 
many dusty particles congregated round a central 
nucleus. Being so minute, the slightest touch, or 
the gentlest breath of air, is sufficient to scatter 
them in thousands, and thus they increase with 
amazing rapidity. The trivial names of blue, 
green, and yellow mould, it may be remarked, are 
of no specific significance, as all these colours are 
common to the species in the different genera, and 
occur even in the same species in various stages 
of its growth. In fact, it is by their different fruc- 
tification under the microscope alone that the dif- 
ferent genera can be recognised, as their mycelium 
or spawn is precisely similar, and to the naked eye 
the appearance they present on the different sub- 
stances which they affect is identical. 
But perhaps the most extraordinary and abnor- 
mal forms of mould are those which it assumes in 
liquids. Fungi, as a class, are confined to solid 
substances ; but there are very few fluids contain- 
ing saccharine matter in which this all-pervading 
mould does not occur. Wine, cider, tinctures, 
syrups, vinegar, catsup, not unfrequently become 
mothery, that is, present the appearance of fibres 
