LANDMARKS OF BOTANICAL HISTORY GREENE 253 



as that natural groups of genera are very numerous; still farther 

 from his mind was such an idea as that all genera may be reduced 

 to a line of natural families. The time was not ripe for the engen- 

 dering of that thought ; nor was it to find expression until three 

 generations later. The list of genera which Tragus can not sys- 

 tematize, as he had done those of the labiates, the crucifers, and 

 the borrages, is a long one. But he must needs bring them all into 

 some kind of grouping, or succession; and the principles upon 

 which he collocates monotypic genera are various. We must take 

 note of several of them. 



There is one quite extended series made up of the following: 

 Convolvulus, two species, Nummularia, Cuscuta, Humulus, Smilax, 

 Dulcamara, Clematis, Bryonia and Lonicera. 1 There is one char- 

 acter, at least a negative one, by whch all these are connectible. 

 Not one of them has an upright stem. All are in some manner 

 climbing; and twining and prehensile plants are much more excep- 

 tional, at least in cool-temperate latitudes where Tragus botanized, 

 than one would suppose. Outside of this series now in hand not 

 many were known to him; for the series does not end with Lonicera. 

 To that there immediately succeed all the genera of cucurbits 

 that are rough-leaved and are grown in gardens. 2 The smooth- 

 leaved and unvigorous or delicate genera Bryonia and Momordica 

 had not yet gained recognition as members of the Cucurbitacecs. 

 And if neither the twining leguminous plants nor the tendril-bearing 

 are placed in this succession, it is for the reason that in their case, 

 and ages befor Tagus, the principle of stem-posture had been 

 subordinated to the higher one of their agreement with the up- 

 right and bushy kinds in a peculiar and distinctive morphology of 

 flower and fruit. Tragus was perfectly aware of all this; and can 

 not have had so much as a thought of including in this present line 

 the weak-stemmed and prehensile peas and beans. 



Sometimes one finds him placing two generic types in juxtaposi- 

 tion for no botanical reason, but only for what may be called a 

 literary motive. The vine, the fig tree, the palm, the olive, and the 

 bay are types not genetically interrelated 3 ; neither to Tragus' 

 knowledge was any one of the five related to any other tree. But 

 in ancient history and poetry all had often been associated. They 

 form a group, and that most historic and distinguished, but on the 

 basis not of botany but of literature. And yet, as regards the after 



1 Stirp. Comm., pp. 804-823. 



2 Ibid., pp. 824-835. 



J Ibid., pp. 1049-1056. 



