THE OBIGIN OF FLORAL APPENDAGES. 135 



stipma nearly blocking up the tube ; and while in the former 

 the irritation set up by the proboscis of an insect has 

 (presumably) given rise to a glutinous secretion, in the latter 

 it has caused a development of hair.* 



Did we but know what the insects were, and how they 

 have poised themselves upon the flower, and in what way 

 their proboscides and tongues have irritated the different 

 parts, one might be able to describe more accurately the 

 whole process ; but that such has been the cause and effect, 

 as above described, seems to me to be too probable a theory 

 to be hastily discarded in the absence of a better one. 



It is one of those arguments of deduction that escape 

 the opportunity of verification, and can only rest for support 

 upon the number of coincidences which can be found, and 

 which collectively furnish a probability of a high order. 



When, then, we find that these processes always occur 

 just where we know the heads, legs, bodies, and proboscides 

 or tongues of insects habitually are placed and irritate the 

 flower, we are justified in recognizing, not only a coincidence, 

 but a cause and effect, though we may not be able to trace 

 the action in each individual case. Thus, it may be asked, 



* The remarkable fact of Heliotrope being the solitary exception 

 oat of the order Apocynacea, with the stigma forming a circalar rim 

 below the summit, may meet with its interpretation from a like caose. 

 The corolla is so folded round the style that it leaves no space between 

 it and the latter. Hence it may, perhaps, have been dae to a similar 

 "Tabbing," that has transferred the stigmatic surface from the now 

 abandoned apex to a lower level, just where the style-arms ought to 

 begin to diverge. The papilte, too, difEer from the ordinary form in 

 being pointed like fine hairs. The relative differences in the distribntion 

 of the papillae on the style-arms of the Compositw, I would also suggest 

 as having been brought about by different insects which irritate them 

 in various ways. So, too, the diverging stigmas of insect-fertilised 

 cruciferous flowers may be compared with the small globular form of 

 self -fertilising species of the Cruciferae. 



