DECOMPOSITION OF PLANTS. 
88 
accomplished by the agency principally of other ani- 
mals, or animated creatures ; so, in the vegetable world, 
vegetating substances usually effect the entire decom- 
position : for though, in the larger kinds, the high and 
lofty ones of the forest, insects are often the primary 
agents, yet other minute substances are commonly found 
to accelerate or complete the dissolution. Fungi in 
general, particularly those arranged as sphaeria, trichia, 
peziza, and boletus, appear as the principal and most 
numerous agents, and we find them almost universally 
on substances in a certain state of decay, or approxi- 
mation to it; though there are a few genera of this 
class which are attached to, and flourish on, living ve- 
getation. The primary decline is possibly occasioned 
by putrescence of the sap, or defective circulation, and 
this unhealthy state of the plant affording the suitable 
soil for the germination of the parasitic fungus; for 
there must be an original though inert seed, till these 
circumstances vivify its principle. By what means the 
parasite finishes the dissolution is not quite obvious ; 
but of that insidious race the byssi, of which family is 
the dry-rot (byssus septica), the radicals penetrate like 
the finest hairs into the substance, and thus destroy the 
cohesion of the fibres. So do the nidularise, many of 
the agarics, the boleti, and others ; and it is not unlike- 
ly that this operation is the general principle of action 
of the whole race, though not so obvious in the minuter 
kinds. These terminators, many of which present but 
little character to the naked eye, under the microscope 
we find to be of various forms, though not always so 
distinguishable from each other as the flowers of our 
garden. Some of the genera of plants appear to have 
distinct agents assigned to them, and the detection and 
enumeration of them have been carried to considerable 
extent by some of the foreign naturalists ; but, to point 
out the variety and curious organization of these sub- 
stances, we will only instance four, to be found on the 
common plants of the garden or the copse : the laurel, 
the elm, the sycamore, and the beech. 
The laurel (prunus laurocerasus) is not, properly 
speaking, a deciduous plant, though it casts its leaves 
