THE GLAUCOUS BIRTHWORT. 83 



The different manner in which vegetables exert 

 their organic powers to effect the destruction of in- 

 sects, is not perhaps unworthy of a brief notice ; some, 

 as those above mentioned, accomplish it by means 

 of elastic or irritable actions, adhesive substances, 

 and so forth; but we have another plant in our green- 

 houses, the glaucous birthwort (aristol. glauca), that 

 effects these purposes without any of these means, 

 but principally by conformation . The whole internal 

 surface of the tubular flower is beset with minute 

 strong spines, pointing downwards ; these present no 

 impediment to the descent of the animal which may 

 seek for the sweet liquor lodged upon the nectarium at 

 the base of the blossom, nor is there any obstruction 

 provided for its return by means of valves or con- 

 tractions, the tube remaining open ; but the creature 

 cannot crawl up by reason of the inverted spines, 

 and to prevent its escape by flying up the tube, the 

 flower makes an extraordinary curve, bending up 

 like a horn, so that any winged creature must be 

 beaten back by striking against the roof of this 

 neck as often as it attempts to mount, and falling 

 back to the bulbous prison at the base of the flower, 

 dies by confinement and starvation, and there we 

 find them : a certain number of these perishing, the 

 blossom fades and drops off. 



All the varieties of this snapdragon have the 

 power of maintaining a state of vegetation in great 

 droughts, when most other plants yield to the in- 



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