7 6 ON NEES VON ESENBECK's 



Like other Monopetake irregulares, the Acanthaceee present consider- 

 able difficulties in working from dried specimens. The corollas are 

 generally of a delicate texture, and not easily softened without injury, 

 their precise forms are difficult to ascertain, and they are often so few 

 on a specimen that the observations made upon one can seldom be veri- 

 fied upon others. Professor Nees has met these difficulties by great 

 care and patience, and his descriptions are conscientiously exact, and 

 directed to such tangible points as the specimens afforded. 



There are indeed numerous cases where allied species, which he con- 

 sidered as sufficiently distinct in the specimens he examined, have 

 proved wholly untenable when attempted to be marked out among the 

 far greater mass now in the Kew Herbaria ; but in this respect Pro- 

 fessor Nees has not gone near so far as some other modern systema- 

 tists, and moreover that is a question upon which there is, and always 

 will be, considerable difference of opinion. What is really to be re- 

 gretted is the excessive multiplication of genera upon characters which 

 all botanists who have worked after him have failed to appreciate, and 

 of which it would appear he could not himself have had any very clear 

 conception. 



There is no doubt that the limits of the old genera Ruellia, Justicia, 

 Barleria, Dicliptera, etc., were vague and ill-defined, and that they 

 each included a vast heterogeneous mass which required grouping and 

 separating upon a large scale ; and, in as far as separating is concerned, 

 Professor Nees has been most laborious in the search for available cha- 

 racters. But that was not all that was required. In a mass of near 

 1500 species (reducible probably on a careful revision to below 1200), 

 it was not enough to establish about 150 mostly small technical genera ; 

 it was necessary to form a more limited number of large natural groups, 

 as well defined as circumstances admitted of, call them genera, tribes, 

 or subtribes, and in this he appears to have failed. His work was ana- 

 lytical, not synthetical, and this was perhaps a necessary consequence 

 of the way in which he proceeded. He did not go through the whole 

 at once; he began with the East Indian ones, established numerous 

 genera without reference to American forms, then took up African and 

 afterwards American Acanthaceee, and, when he came to work the whole 

 together for the « Prodromal,' appears to have been far too much com- 

 mitted to these special isolations to condense them upon new principles 

 into any more general and natural groups. This is an operation we 



