DIFFERENTIATION 



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type are regarded as a response to the stages in the differentiation 

 of the conditions. 



Although there are still primitive families, like the Composite, the 

 Cyperacece, etc., that occupy most of the globe, there are others 

 where differentiation has proceeded so far that the original family 

 type is lost. The lost type is then only represented in the characters 

 that join together a number of families in a great plant-group, which, 

 though they hold the world between them, respectively characterise 

 different regions of it. There are several such alliances, and some 

 are referred to in this connection in the author's Victoria Institute 

 paper. Reference has already been made to the closely related 

 families of the Primulacece and the Myrsinacece that between them 

 range the globe, the first in the temperate regions and the second in 

 the tropics. A similar example is offered by the Geranial alliance, 

 of which the two oldest families, the Geraniacece and the Oxalidacece, 

 divide the world between them, the first being most characteristic 

 of the temperate zones and the last of the warmer regions of the 

 globe. The great Scitamineous alliance illustrates the same prin- 

 ciple in the warm regions of the world. Though there is no general- 

 ised type now known, we find it represented in the characters common 

 to the four closely connected families that range over warm lati- 

 tudes : the Zingiber acece mainly in the Old World, the Cannacece and 

 Marantacece mainly in America, and the Musacece fairly well shared 

 between both hemispheres. 



But the recognition of this principle is not always easy, especially 

 in those cases where, as in the Pandanacece, we have a family restricted 

 to the tropics of the Old World with no very near relations in the 

 New World. Though kindred families are not altogether wanting, 

 it would be justifiable to presume that the families originally asso- 

 ciated with it disappeared long since in the differentiating process. 

 Where special influences have been at work rapidly disguising the 

 characters of the primitive family, as in the case of the alliance of 

 the insectivorous families, Sarraceniacece, Nepenthacece and Droseracece, 

 it would seem that a wide gap must separate them from families of 

 the same parentage that never acquired this habit. It would not 

 appear that we could establish any direct connection between the 

 cosmopolitan Droseracece as the mother family and the closely 

 related American Sarraceniacece and Asiatic Nepenthacece as the 

 offspring. 



In the family, in the tribe, in the genus, in the species, and in the 

 variety and local race, we see the same principle at work; and to 

 illustrate it we will draw nearly all our examples from the same 

 plant-type. We see it in the fact that the Geraniacece which has 

 given its name to an alliance of families, still holds most of the area 

 of the primitive world-ranging type. We see it in the behaviour of 

 the tribes within the family. Here the tribe Geranice, which comes 

 nearest to the primitive form, has by far the greatest range, covering 

 as it does nearly the entire area of the family. We see it in the 

 genera of this tribe, where Geranium, the most primitive of all, the 

 genus that lies farthest back in the line of descent, is the genus most 

 widely distributed, occupying as it does nearly the range of the tribe. 



