2126 A TEXTBOOK OF THEORETICAL BOTANY 



linear leaves. Although classified as a variety it reverts under cultivation to 

 the typical plant of the species and is therefore no more than a form. The 

 second example is Cytisus scoparius Link var. prostratus Bailey. This was 

 originally classified as a variety, was reduced to a form by several later 

 systematists and has now been shown by Turrill to come true from seed in 

 cultivation and to be therefore a stable variety. 



The attempt to distinguish between variety and form rests on the 

 assumption that there are two sorts of morphological characters. They were 

 called " ecad " and " phyad " by Griesbach or " epharmonic " and 

 " filiated " by Vesque. The first category are assumed to be directly related 

 to the environment, the second category to be almost wholly hereditary. 

 Some systematists deny the validity of the distinction and if indeed it 

 cannot be upheld then the separation of variety and form loses its only 

 rational basis. 



Jordan in 1864 administered a shock to the classical systematists by his 

 examination of the small Crucifer, Erophila verna. He described fifty-three 

 types, later (1873) increased to about 200, all within the same morphological 

 " species", the great majority of which he cultivated and showed that they 

 maintained small but permanent heritable distinctions. This originated the 

 idea of the microspecies, or Jordanon, as Lotsy called it, in opposition 

 to the macrospecies, or Linneon. It was the first notable example of the 

 clash between Museum and Natural Taxonomy. Obviously if any con- 

 siderable percentage of the macrospecies can be dissected in this way, then 

 the macrospecies is only an abstraction and, unless the test of cultivation can 

 be employed, the ground is cut from under the systematists' feet. The 

 problem has stimulated a great deal of theoretical examination of taxonomic 

 principles, but in practice it has been largely met by ignoring it. Winge in 

 1940 reduced Jordan's types of Erophila to four, on cytological grounds, 

 and concluded that the apparent multiplicity of types was due to hybridiza- 

 tion and to permutations in the genetic combination of their characters. 

 This certainly simplifies the issue in this case, but many others remain, 

 and basically the principle is the same, whether there are only four types or 

 four hundred, that the morphological macrospecies contains distinct groups, 

 which are permanent and natural units, but which cannot be adequately 

 comprehended by morphological methods, though morphology may, and 

 often does, give evidence of their existence, so that museum microspecies are 

 now an accepted systematic category. The term " sub-species " may 

 mean the same thing, or it may in other cases be a transitional assemblage, 

 part of a series between two geographically or ecologically separated groups. 

 It is, once more, a subjective concept. 



Natural Species, or as some prefer to call them. Experimental Species, 

 are not all of similar size or of equivalent grade. The causes of discontinuity 

 between them are various, and complete discontinuity is not always achieved 

 at one step. There is an hierarchy of minor groups among them, some of 

 which represent developmental stages, and their discrimination is often a 

 difficult matter involving ecological, genetic and sometimes immunity tests. 



