I4t5 PLANT STUDIES 



amount of damage to plants, ^^funy Lurrowing animals 

 attack subterranean parts of plants, and interfere seriously 

 with their occupation of an area. 



Various proteetivo adaptations against such attacks have 

 been ]X)iiite(l out, l)ut this su1)ject probaljly lias been much 

 exaggerated. TIk^ occui-ri'ni'e of hairs, i)ric.kles, thorns, 

 and spiny growtlis upon many plants may disc'ourage the 

 attacks of animals, l)ut it would be I'a.sli io a.ssume that 

 these protections have been developed because of the danger 

 of such attacks. One of the families of jila.nls most com- 

 jaletely protected iu this way is the great cactus family, 

 chiefly inhabiting the aiid regions of soutliwestern United 

 States and IMe.xieo. In such a region succulent vegetation 

 is at. a premium, and it is doulitless true that the armor of 

 tluu'us and bristles reduces the a,mount. of destiaiction. 



In addition to armor, the acrid or bitter secretions of 

 certa.in plants or certain parts of ]ilants would have a 

 tcmlency to wai'(l dtf the attacks of aJiimals. 



lOlJ. Plant rivalry. — It is e\iilent lliat ilu're must bo 

 rivalry aiuong pbinis in dceujiyiiig an ai'ea.. and that those 

 plants wlii<'h can most nea.r]y utilize ideutii-il (^oiulitions 

 will be the most intense rivals. l-'or example, a great many 

 young oaks may start U[i over an a.i'ea. and it is e\ idi'ut 

 that the individuals must come into sharp cumpetitidii with 

 one a.nntbei', and lliat but few of them succeed in establish- 

 ing tliemselves ]>i'rmaJU'iilly. 'I'his is ri\ali-v between in- 

 <li\'iduals 1)1' Ihe same kiud ; but some otbci' kind of I I'ees, 



as llie 1 -b, may conu' into c(jiupetit ion witli the oal^, and 



anolliei' form of ri\'alry will ajtpea.r. 



As a. conse(|uence (if plant i-i\"alrv. the dilTei'enl plants 

 which linally sui'ceed in lakiug ]iosscssiiiu of an area, are 

 a])t to be dissimilar, and a jilani sociely is usually made U}i 

 of plants wliicb repi'escnt widcl v di ITerent reu-ions of the 

 pla.nt kingdom. 1 1. is sonu'limes said tliat any "well de- 

 veloped jibiut society is an epilmi f Ibe plan! kin^-iloni. 



A familiar illustration of jila.nt i-i\ali-y ma\' be obser\ed 



