CHAP, xcviii THE WEAPONS OF SPECIES 367 



struggles a very great part is played by such conditions as, whether one 

 species demands more light or withstands more shade, or better endures 

 moist soil or moister air or drier wind than other species ; but likewise of 

 great import are the conditions as to whether a species grows more or 

 less rapidly than its rivals, or whether in this respect it behaves differently 

 in its youth and old age. Other crucial conditions are not only whether 

 the nutritive contents of the soil are more suited to one species or to 

 another, but also whether the one bears more seeds, becomes reproductive 

 at an earlier age, possibly multiplies more freely in a vegetative manner 

 by suckers or propagative buds ^ ; whether its seeds preserve their power 

 of germination for a long or short time ; whether or no the seeds germinate 

 more easily, what arrangement and pose are assumed by the branches, and 

 what is the general type of architecture ; whether or no the roots and 

 rhizomes are strongly branched and densely matted ; and so forth. Thus 

 the biological and other characters of growth-forms, in addition to many 

 of the factors discussed in Section I, are of great significance in the struggles 

 between species ; sometimes one species gains the lead over another by 

 means of some almost imperceptible advantage. 



But in addition to the vital characters pecuhar to different species 

 other conditions are of importance in these struggles, for instance : attacks 

 by parasitic fungi, and by insects or other animals (mice in forests, and 

 the hke), presence or absence of animals burrowing in the soil (for instance, 

 earthworms ^), and, in short, the conditions prevaihng in regard to all 

 organisms beneficial or harmful to plants. 



The general statement can be made that a species has the greater 

 probabihty of emerging victorious from its struggle the greater the extent 

 to which it finds itself in its optimal area, or in other words, the more 

 numerous are the ecological conditions best suited to it. Consequently 

 a species has always to engage in its hardest and most exhausting struggles 

 at the boundaries of its distributional area, if it has here reached 

 the utmost hmit of its wanderings as determined by climate. The more 

 suited is the chmate to a species, the less exacting is this as regards soil and 

 other conditions, and the more capable it is of competing with rivals. As 

 a pertinent example may be cited the fates of pine and spruce, as already 

 described on p. 354. If a species of tree be burned down or felled on 

 a station lying within its optimal area, it will as a rule reoccupy the 

 denuded spot if this be not artificially interfered with ; but if it meets 

 with this fate outside the area of its best growth, then it will not reappear, 

 but its place will be taken by a species of tree in whose optimal area the 

 station is situate.^ 



It may be mentioned that some species when producing formations are 

 not in their optimal sites. Alders attain their most luxuriant development 

 on well-drained soil. But they are usually expelled from this by other 

 competing trees. Only in swamps, where they do not thrive so well, are 

 they dominant. In like manner Calluna vulgaris flourishes upon rich 

 soil better than on poor soil, but it is excluded from the former by com- 

 peting species. On Madeira Vaccinium maderense shows its strongest 

 growth in the region of laurel- maqui, where it is rare, and does not produce 



' See the remarks on social species, pp. 92, 139. ' See pp. 78, 363. 



* Mayr, 1890. 



