LANDMARKS OF BOTANICAL HISTORY GREENE 247 



Tragus Modern 



1 . Nasturtium hortense Lepidium sativum 



2. Nasturtium aquaticum Nasturtium officinale 



3. Nasturtium pratense Cardamine pratensis 



4. Thlaspidium Lepidium ruderale 



5. Alliaria Alliaria officinalis 



6. Thlaspi Thlaspi arvense 



7. Lepidium Lepidium latifolium 



It will be seen at a glance that no taxonomic account is made 

 of the pods in drawing up the line of those crucifers. Siliculose 

 and siliquose genera are completely intermixed. It is just what 

 Sachs, from his mistaken point of view, calls a "motley order." Yet 

 there is a system in the arrangement of these seven crucifers, 

 and it is plainly apparent. Draw a line between the numbers 4 

 and 5 and all above the line are compound-leaved, all below it 

 simple-leaved. It is a natural arrangement, according to Tragus' 

 notions certainly very crude, sometimes about the tests of 

 affinity. From this point, however, the succession of members of 

 this family is broken by the intrusion of eight species belonging to 

 three other natural groups. The intruders are, two persicarias, 

 five buttercups, and a rather peculiar plantain. Only at the end of 

 such a line as this does he again take up the crucifers. 



If in this procedure the German father seem chargeable with 

 having abandoned the principle laid down in his Preface, I see no 

 clear defense for him. If he had been intent upon collocating things 

 by the criterion of "form," as he calls it, he must needs have kept 

 the line of the crucifers uninterrupted by plants polygonaceous 

 and ranunculaceous. He was botanist enough easily to have seen 

 the marked contrasts of form between these plants and those cruci- 

 fers that flank them in considerable file on either hand. Being such, 

 these intrusions were not made by chance or whim. Apparently 

 it is a case of the subordinating of taxonomic principle to the 

 convenience of a multitude of those to whom morphologic marks 

 would go for naught, and with whom a grouping according to use- 

 ful qualities would be welcome. Let us understand how, with such 

 a purpose before him, Tragus would not unnaturally break the 

 succession of crucifers and interpose a line of buttercups. 



Where the succession of square-stemmed opposite-leaved aroma- 

 tic herbs ends in a fragrant teucrium, and the terete-stemmed 

 alternate-leaved series begins with the garden peppergrass, I have 

 characterized the transition as abrupt; but this was done with a 



