PHYTOGRAPHIC EXPRESSIONS AND ARRANGEMENTS. 191 



Besides a few limited local '• Floras " exist for portions of the 

 English and German and perhaps other countries, but they 

 cannot be referred to critically on this occasion, as these small 

 works are not accessible here. 



The advantages of using a simple dichotomy are, to trace out 

 quickly the name of any plant irrespective of gaining thereby any 

 fuller direct knowledge of its characteristics — further to render 

 thus far any lengthened study of marks of distinction unnecessary; 

 the disadvantages are the scattering of the characteristics, the loss 

 of view over their complex, the difficulty of seizing again the thread 

 of affinity if once lost, and the rupture of the chain of natural 

 affinity. It has on this occasion been endeavoured to secure all 

 the advantages of the plan and to remove all the disadvantages. 



The great difficulty of the method consists in singling out 

 successively solitary, invariable and very obvious marks of 

 distinction, by which one order or one genus or one species can 

 be surely separated after another, until positions — always in 

 a dual contrast — are exhaustively provided for all of them ; and 

 further to effect this uninterruptedly and yet systematically ; 

 whereas in ordinary treatment of plants, and indeed also of animals 

 for descriptive Floras and Faunas, several cardinal notes are put 

 together diagnostically, just as in medical science the complex of 

 the symptoms gives the diagnosis of the disease, any single one 

 possibly masked, though perhaps only exceptionally so. 



In elaborating here such a plan of dichotomy, it became 

 necessary, to construct for the complex of orders, of genera and 

 also of species, whenever numerous, a tabular arrangement, 

 somewhat like genealogic scales, so as to render the conspect easy 

 at a glance ; it is contemplated, to issue these tables hereafter in 

 an Atlas-form, according to a design adopted by Meissner for his 

 "Plantarum vascularium genera," (1836 - 1840). The expediency 

 of using a mere negative or some evasive expression or any general 

 positive is never resorted to in the work now offered, for over- 

 coming any difficulty in pairing off the main-passages, which to 

 effect clearly and contrastingly is the real gist of the whole method; 

 while its principal success must be sought in avoiding, that the 

 species of plants and also their genera and orders do not become 

 scattered regardless of natural alliance in perhaps a chaotic 

 manner, that propositions are chosen which do not combine the 

 utmost briefness also with logical comprehensiveness, and that the 

 dichotomic notes, which are to carry over to the next passus, are 

 wanting in obviousness and perfect reliability. 



The organographic expressions, which we use at the present 

 time, originated already — though only to a very small extent — 

 with the ancients, who however did not even apply the terms 

 always in the present interpretations ; these terms were somewhat 



