18709. } Instinct and Reason. 103 
class of propagating agents are secondary or non-essential, the 
latter the essential organs. The former passive agents, the latter 
active. 
Thorns, briers, nettles, etc., are also passive elements of defence. 
For offence many plants have a singular apparatus, especially 
that curious class of plants termed insectivorous, or carnivorous, 
hereafter to be discussed. 
But the plant demands food. This it obtains in a peculiar way. 
Its anatomy and physiology are adapted to that peculiar way. It 
does nothing contrary to nature with impunity. Mode of growth 
in all plants tend to the same end. Hence the lowest as well as 
the highest can do no more than supply wants ; seek a situation 
best suited to its growth and development; remove or avoid 
obstacles interfering with growth, and reproduce its kind in due 
time. For this purpose certain organs are exercised, and this con- 
stitutes the functions of a plant. 
In plants, as well as in animals, we everywhere perceive the 
operation of the law which secures to them what naturalists term 
“the survival of the fittest.” The weaker must succumb to the 
stronger, and disappears, is annihilated, when the struggle for 
existence becomes too great for that form of plant life. 
Plants which need much air (or elements of air) and light, and 
moisture, are found in situations most favorable for obtaining 
them ; if deprived of them the result is obvious. 
In the case of most terrestrial plants, a suitable depth and 
character of soil are required. If the soil be too poor in the 
elements of nutrition required by a peculiar kind of plant, or in 
excess, or the soil too dry or too light, the different elements 
must be duly supplied or apportioned, and sufficient moisture 
furnished by irrigation lest the heat of the sun destroys the roots 
of the plant. The same principles are observed in respect to all 
the classes of the flora spread over the earth. Warmth implies 
light or sunshine, and where it is wanting none but the lowest 
orders, like the lichens and alge, survive. The different climates 
also possess their own vegetation, and even in different regions of 
the same zone we find plants totally distinct from each other. 
Hence circumstances, as well as conditions, must find a place 
among the demands of a plant. 
For the removal of obstacles the plant has two courses, to dis- 
integrate the object opposed to its progress, absorbing it if it be — 
