CHAPTER IX 



THE STRUGGLE FOR EXISTENCE 



100. Definition. — Tlie phrase ''struggle for existence" 

 has come to mean, so far as ])huits are concerned, that it is 

 usually im|M>ssilile for them to secure ideal relations, and 

 that they must encounter unfa.vuralile conditions. The 

 proper light a.nd lieat relations may lie ditlicult to oljtain, 

 and also tlic pi-o])cr relations tc food matciial. It often 

 ha.p}>cns, also, that ('(jnditioi^s once fairly favorahle may he- 

 comc unfa,V(>rable. Also, multitudes of jilants ai'e trying 

 to take possession of the sa.me conditions. All this leads 

 to the sii-callcd " sti-uggle," and vastly mui-c plants fail 

 tlian siu'cccd. licfore considering the oi'gaiuzal icn (if plant 

 SDcieties, il will he liel])ful to consider some of the jiossiiile 

 changes in condilKins. and the elfect on plants. 



101. Decrease of water. — This is pi'oliahly tlu' most com- 

 mon factor lo lliictuate iu tlie environment of a. plant. 

 Along tlic liordcrs of streams and ]ionds. and in swampv 

 places, tlic \ariation in thevalci' is very iioliccahlc. liut the 

 same tiling is t laic of soils in gcnci'al. I iii\vc\'ci\ the (dninge 

 cliielly i-cfei'i-cd to is ihat. which is ])ci-m;iiient . and which 

 coiri])cls [ilaiils not merely to tiile o\cr a. droiiij-ht. hut to 

 face a, ]iei'nia.ncii t decrease in the w;i(cr siipplw 



Ai'ound t he m;irgi lis of ponds ai'c \rv\ comnioid v seen 

 fi'inges of snch phiiils as Imlnishcs, cal-lidl lliiu's, rec(l- 

 grasses, etc.. st;iiidiiig in slmnl w;iter. .\s these [ilants 

 gi'ow (dose togct lici', silt from the land is entangled hv them, 

 and pi-csi'nth' it .-ic.'umul.-itcs to such ;in extent that there 

 is no more standing waler, and the water su|iplv for the 

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