120 



TAXONOMY. 



its first appearance, we perceive that it was intended to have 

 been a branch, which has only proved abortive, and whichj 

 notwithstanding, even as a spine, bears leaves, and, in Euphor- 

 bia heptagona, sometimes flowers and fruit. 



179. 



To avoid mistakes, we also often follow analogy or in- 

 duction. When a form is common to several families, we 

 cannot mistake its sign, even when it seems to fail. Thus, 

 as the Orchideae are related to the Scitamineae and Irideae, we 

 find in the former the sign of the three male organs, in the 

 two lateral appendages of the column of fructification, or the 

 Staminodia of Richard. In like manner, the two fibres, 

 which Gratiola carries beside the fruitful filaments, will ap- 

 pear to be abortive filaments, when we compare them with 

 the other Scrophulariae, which sometimes have four fruitful 

 filaments, and sometimes, in addition to these, even a fifth. 



The same analogy which leads us from genus to genus, ex- 

 plains also one species by another. As in the Leea we con- 

 sider the cleft scales, with which the filaments are inter- 

 mingled, to be abortive filaments, because in the nearly re- 

 lated genus Melia ten filaments have perfect anthers ; we 

 also conclude that Polygonum amphibium, which has only 

 five, and Polygonum per sicaria, which has only six filaments, 

 have lost the rest by abortion, because several species of the 

 same genus possess eight filaments. 



180. 



From abortion principally arise the many irregularities in the 

 structure of plants ; because we may suppose that the original 

 formation of natural bodies is regular. When we thus find 

 unimportant irregularities in the organs of a plant, we may 

 suspect that there are plants in which these irregularities as- 

 sume a more marked aspect, — that there are others where 

 these organs are completely abortive, — and others in which 

 complete regularity takes place. The usual form of the pa- 

 pilionaceous flower is very irregular in Dimorpha ; the vexil- 

 lum and carina in AmorpJta are completely aboi tive ; and in 



