GENERAL INTRODUCTION 2*3 



written at length on these formations, and despite the 

 extravagancies to which some theorists have pushed the 

 principle, in itself the theory is unquestionably true. 



For example, the alpine Aster is found allied with 

 Erigerons, Leontopods, Saxifraga aizoon, etc. ; Viola 

 cenisia makes its home among chalky rocks alongside 

 Thlaspi rotundifolia, Ranunculus parnassifolius, Tbalictrum 

 saxatile, J^ernera saxatilis, Adenostyles leucophylla, etc. But 

 why ? Undoubtedly because these species find in one 

 place the conditions necessary to their existence, not 

 simply from a craving for the association. Some there are, 

 however, which seem to obey a mutual attraction and so 

 seek to unite in excluding from their territory strangers 

 to the colony. For example, mark the Rhododendron 

 ferrugineum, girdling our alps with a broad and solid 

 belt, in arrogant lordship of the ground and soil where 

 it grows. Yet into fellowship are admitted some few 

 relatives and friends : diverse Vaccinia, Gentiana purpu- 

 rea, Gymnadenia albida come within the circle and shelter 

 in the owner's shade. So the dwarf juniper welcomes 

 the common Heath (Erica vulgaris), Lycopodium alpinum 

 and clavatum, Campanula barbata and Scheuchzeri, Jlrnica 

 montana, Jiypochxris, Anemone alpina and sulfurea. Jlzalea 

 procumbens may often in selfish egoism spread acres-wide 

 her broad horizontal sheets ; yet modest plants find 

 shelter there, Potentilla aurea, Phyteuma hemisph&ricum, 

 Empetrum nigrum, etc. Not less assertive are some of the 

 willows, Salix herbacea, retusa, reticulata, serpylli folia. In 

 self-contained colonies of straggling shrubs, whoseflatten- 

 ed branches often rise but a few inches from the ground, 

 they clothe wide stretches of high alp. Whole domains, 

 again, are monopolised by swards of grasses or of sedges, 

 associated, however, with plants which can do them 

 useful service in repelling all that is hurtful or unprofit- 

 able. These are true colonies, zealously maintaining the 



