BOTANICAL GAZETTE. 



Vol. IV. OCTOBER, 1879. No. 10. 



The beheading of flies by Mentzelia ornata. — In the BuUetin dc 

 la Societe Botanupie de France, vol. xxiv, 1877, p. 26-30, is an account, 

 by M, J. Poisson, of his observations upon Mentzelia (Bartonia) ornata, 

 as cultivated in the Jaidin des Phmtes, Paris, and the very singular 

 mode in which it causes the destruction of flies. This account, until 

 now, had escaped my notice. It is so curious that I here recapitulate 

 the essential points of M. Poisson's communication, in the hope that 

 observations mav be made in this countrv, either bv the feAV who are 

 able to cultivate this ornamental plant with success, or by those who 

 can examine it in its native stations. It is well known that the 

 roughness of this and some related Loasaccw is owing to the stifl" 

 bristles of the surface being provided with an armature, at certain 

 points along their length, of retrorse barbs. There are three or four 

 whorls of tliese barbs, and four or five barbs to each whorl, on the 

 larger bristles; in the smaller there is onl}'- a terminal whorl of barbs, 

 in the manner of a glochidiate bristle. Mixed with these harpoon- 

 like bristles are some soft ones, tipped with a capitate gland, which 

 secrete a viscid matter attractive to insects. It apj^ears that ilies so 

 attracted thrust in their proboscis between the thickly set glochidiate 

 bristles to feed upon the secretion of the glands between and below. 

 The retrorse '"barbs interpose no obstacle to this ; but when the pro- 

 boscis is withdrawn, its dilated and cushion-like tip catches in the 

 barbs, and holds all fast. The harder the backward pull, the firmer 

 and the more extensive the attachment to the sharp barbs: the 

 wounded and impaled organ becomes congested and swollen ; and 

 the insect is seldom able to disengage it. Especially is this the case 

 with the larger Hies. Some i)erish by exliaustion ; but more of them, 

 passing round and round in a circle and in one and the same direc- 

 tion, come to an end by twisting off their heads! Dried specimens 

 of the plant in herbaria exhibit many small coleoptera and the debris 

 of various other small insects, but these have been caught bj- their 

 feet or mandibles or other parts. Insects too small to be impaled on 

 the barbs are held fast by the viscid secretion of the glands, and like- 

 wise perish. In these respects the arrangement comes under the 

 head of those recently illustrated by Kerner, for the exclusion from 



