ORGANS AND THEIR FUNCTIONS 321 
largely because their conditions of life were simpler and so 
their needs less than ours. Similarly we should find the 
higher plants, such as fiax, contrasted most. significantly 
with such lower forms as Irish moss in the extent to which 
they exhibit a differentiation of parts and mutual helpfulness 
throughout; and we should find a similar reason to hold 
good. Accordingly, we may not inaptly compare the roots, 
the stem and its branches, the leaves, and the parts of the 
flowers and fruit of our plant to the various classes of workers 
which we find in a civilized community, since the work of the 
whole is similarly divided among the parts and all labor for 
the common good. It is such an idea as this that naturalists 
have in mind when they speak of the physiological division 
of labor observable in a plant or an animal. 
96. Organs and their functions. In either a plant or an 
animal any part having a special office to perform is called 
an organ, the special office being known as its function.? 
Thus the root of our flax-plant is an organ the chief function 
of which is to absorb mineral substances from the soil. The 
function of ,the stem is mainly to support its leaves, flowers, 
and fruit advantageously; while the general function of its 
floral organs is to insure the production of good seed; and the 
function of its fruit is to bring about their dispersal. We 
often find the same function performed by different organs 
which are curiously unlike in other respects, as for example 
the function of support as performed by the tendrils of 
the pea (Fig. 37), the climbing roots of the poison-ivy 
(Fig. 210), and the grappling prickles of the rattan (Figs. 223], 
II). Organs which agree in function are said to be ana- 
logues * of one another, or to be analogous. According to 
their main functions the parts of our typical plant may be 
classified conveniently as organs of nutrition (e. g., the root, 
foliage, leaves, and cotyledons); of support (the stem and 
its branches); of protection (the bark); of reproduction (the 
1Or’gan < Gr. organon, an instrument or tool. Since animals and 
plants are made up of organs they are called organisms, and the mate- 
rials which are present in them alone are called organic, to distinguish 
them from inorganic or mineral substances. 
2Fune’tion < L. functio, performance. 
3 An’-a-logue < Gr. ana, according to, logos, relation. 
