DESCRIPTION OF PLATES. 153 
definitely if these microscopic plants do not obtain 
access to them. 
The materials drawn from nature’s storehouses, 
— the earth, the ocean, the atmosphere, — for the 
construction of the higher plants and animals, 
would be exhausted in course of time if there 
were no provision for returning them to the com- 
mon stock ; and the surface of the earth would be 
encumbered with the bodies of successive genera- 
tions of animals and with dead but undecayed 
vegetable tissues, were there no provision for the 
decomposition of these organic structures. This 
work of decomposition, however, is provided for, 
and it is accomplished by these microscopic plants, 
which make up for their diminutive size by their 
rapid growth and reproductive activity. But, as 
we have already seen, these little giants do not 
alone confine their attention to dead organic mat- 
ter. They also invade the living structures of 
plants and animals, and appropriate to themselves 
the material necessary for the vigorous growth of 
their host, thus causing disease, and sometimes 
death. 
Fortunately, living protoplasm possesses an in- 
herent power of resistance against these parasites, 
and it is little liable to suffer from their attacks, 
unless enfeebled by age or want of proper nutri- 
ment. The starved plant is more subject to be 
attacked than the vigorous one. The puny and 
ill-nourished child is more liable to suffer from 
parasitic (vegetable) skin diseases than the robust. 
The individual enfeebled by starvation, wasting 
