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 flax, 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 o.ur 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 cfimbing roots of the poison-ivy 

 (Fig. 210), and the grappling prickles of the rattan (Figs. 2231, 

 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 



1 Or'gan < Gr. organon, an instrument or tool. Since animals and 

 plants arc 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. 



2 Func'tion < L. funclio, performance. 



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



