Part 96. Organs and their functions. In either a plant or an animal any part having a special office to perform is called an organ,1 the special office being known as its function.2 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 I, II). Organs which agree in function are said to be analogues 3 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 flower); and of dissemination (the fruit). The first three of these groups, since they have to do primarily with the individual life of the plant, form what is called the vegetative system, while the others being concerned only with propagation and the care of offspring constitute the reproductive system.

1 Or'gan - Gr. organon, an instrument or tool. Since animals and plants are made up of organs they are called organisms, and the materials which are present in them alone are called organic, to distinguish them from inorganic or mineral substances.

2 Func'tion - L. functio, performance.

3 An'-a-logue - Gr. ana, according to, logos, relation.