2 PLANT STUDIES 
numerous as are the conditions of living, and it may be said 
that each society has its own special regulations, which ad- 
mit certain plants and exclude others. The study of plant 
societies, to determine their conditions of living, is one of 
the chief purposes of botanical field work. 
3. Plants as living things. Before engaging in a study 
of societies, however, one must discover in a general way 
how the individual plant lives, for the plant covering of the 
earth's surface is a living one, and plants must always be 
thought of as living and at work. They are as much alive 
as are animals, and so far as mere living is concerned they 
live in much the same way. Nor must it be supposed that 
animals move and plants do not, for while more animals than 
plants have the power of moving from place to place, some 
plants have this power, and those that do not can move cer- 
tain parts. The more we know of living things the more is 
it evident that life processes are alike in them all, whether 
plants or animals. In fact, there are some living things 
about which we are uncertain whether to regard them as 
plants or animals. 
4. The plant body. Every plant has a body, which may 
be alike throughout or may be made up of a number of 
different parts. When the green thready plants (algce), so 
common in fresh water, are examined, the body looks like 
a simple thread, without any special parts ; but the body of 
a lily is made up of such dissimilar parts as root, stem, 
leaf, and flower (see Figs. 75, 144, 161, 169). The plant 
without these special parts is said to be simple, the plant 
with them is called complex. The simple plant lives in 
the same way and does the same kind of work, so far as 
living is concerned, as does the complex plant. The differ- 
ence is that in the case of the simple plant its whole body 
does every kind of work ; while in the complex plant 
different kinds of work are done by different regions of the 
body, and these regions come to look unlike when differ- 
ent shapes are better suited to different work, as in the 
