156 POLYGONUM ARIFOLIUM. HALBERD-LEAVED TEAR-THUMB. 



SO far as to believe that they were later acquisitions, produced 

 according to the law of natural selection. Nor was Dr. Darwin's 

 theory generally accepted; and Anthony Todd Thompson, a 

 famous lecturer, who flourished about twenty years after the 

 appearance of " Phytologia," in controverting the theory in ques- 

 tion, went so far as to say that " most of the notions which our 

 reasonings on final causes lead to, are neither philosophical nor 

 accordant with correct observation, and we must confess our 

 ignorance of the utility of this description of armature in the 

 vegetable economy." It is curious to note in this connection 

 that Dr. Thompson, who, as may be learned from the extract 

 just given, considered himself a champion of exact science and 

 an enemy to fanciful "speculations," was himself looked upon 

 as a mere "speculator" by those who followed Dr. Darwin's 

 progressive views. The modern student, however, although he 

 may, with Dr. Thompson, confess his ignorance of the precise 

 meaning of such armatures as those borne by our Tear-Thumb, 

 docs not consider the solution of the question as absolutely im- 

 possible, and therefore looks upon the thorns as legitimate sub- 

 jects of philosophic study. Some later botanists have regarded 

 them as aids to climbing rather than as a mere protecting coat 

 of mail, and this purpose they certainly serve excellently well, 

 wliatever may have been the object for which they were origi- 

 nall)^ intended. 



In its geographical range within the United States the Poly- 

 goinim arifolium presents some interesting features. It is found 

 in Maine and southward through the Seaboard States to South 

 Carolina, but in its progress westward it avoids the South, and 

 shows a northern tendency. It grows in Ohio, and thence 

 through Michigan and Wisconsin to Minnesota. Prof. Aughey 

 also reports it from Nebraska, but it has not yet been found in 

 any part of Iowa, as far as we know. Its line of distribution, 

 therefore, seems to form two narrow belts, one running due 

 west, the other southwest. 



It is in bloom from July to September, 



