76 INVASION 



fest divergence, and still not be an indication that it is arti^- 

 ficial. "Z 



Darwin (t859:I86), in speaking of convergence, says: "If 

 two species belonging to two distinct though allied genera, 

 had both produced a large number of new and divergent 

 forms, it is conceivable that these might approach each 

 other so closely that they would have all to be classified 

 under the same genus : and thus the descendants of two dis- 

 tinct genera would converge into one." The application of 

 this statement to species would at once show the possibility 

 of polyphylesis in the latter, and a further examination of 

 the matter will demonstrate its probability. It is perfectly 

 evident that a species may be split into two or more forms 

 by varying the conditions, let us say of water-content, and 

 that the descendants of these forms may again be changed 

 into the parent type by reversing the process. This has, in 

 fact, been done experimentally. Since it is admittedly im- 

 possible to draw any absolute line between forms, varieties 

 and species, it is at once clear that two distinct though re- 

 lated species, especially if they are plastic, may be caused 

 to converge in such a way that the variants may constitute 

 a new and homogeneous species. This may be illustrated 

 by a concrete case at present under investigation. Kuhn- 

 istera purpurea differs from K. Candida in being smaller, in 

 having fewer, smaller and more narrow leaflets, and a 

 globoid spike of purple flowers in place of an elongated one 

 of white flowers ; in a word, it is more xerophytic. This 

 conclusion is completely corroborated by its occurrence. 

 On dozens of slopes examined, Kuhnister a purpurea h&s never 

 been found mingling with K. Candida on lower slopes, except 

 where an accident of the surface has resulted in a local de- 

 crease of water-content. The experiment as conducted is a 

 simple one, consisting merely in sowing seed of each in the 

 zone of the other, and in growing K. purpurea under con- 

 trolled mesophytic conditions, and K. Candida under simil- 

 arly measured xerophytic conditions in the plant house. 



While the polyphyletic origin of species is in a fair way to 

 be decided by experiment, it receives support from several 



