2 PLANT STUDIICS 



nnmerous 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 nf liotaviical 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 })lant covering of the 

 earth's surface is a living one, and plants must always lie 

 thought of as living and at work. They are as much ;dive 

 as are animals, and so far as mere living is concerned they 

 live in much the same way. Nor must it be supjjosed tliat 

 animals move ami jilants do not, for while more animals tluin 

 plants have the })ower of moving from jilace tij place, some 

 plants have this power, and those that do not can move cer- 

 tain parts. The more we know of living things the morels 

 it evident that life processes are alike in them all, whether 

 ]ilants or animals. In fact, there ai'e s(jme living things 

 aljout which we ai'c uncertain whether to regard them as 

 plants or animals. 



4. The plant body. — Every plant has a body, whicli may 

 be alike througlmut or may be made up of a nundx'r of 

 different parts. W'licu the green llircaily plants (uhjir). so 

 common in fresh water, are examincil, (he liody looks like 

 a simple thread, wit.hout any special ]iarLs ; Init the body of 

 a lily is made up of such dissimilar ]ia.rts as root, stem, 

 leaf, and flower (see Figs. 7,5, f44. fGf, HV,)). Tlie plant 

 without these sjiecial jiarts is said to be .'<i//i/ilc. tlic plant 

 with them is <'alled roiiijilej'. 'J'be simple plant li\cs in 

 the same way and does the same kind of work, so fai' as 

 living is concei'in_Ml, as does the complex plant. The tlilVcr- 

 cnce is that in the case of the simple phint its whole lioilv 

 does every kiml of work ; while in the complex plant 

 different kinds of work are done hy dilfcrent regions of the 

 body, and these regions come to look uidike wlien dilTer- 

 ent shapes are better suited to dilfei'cnt work, as in the 



