AROIDEAE 



489 



the spadix projecting from it, serve to attract minute midges, particularly those of 

 the genus Psychoda. The decomposing, urinous smell of the inflorescence during 

 anthesis is a further attraction. The ventricose lower part of the spathe forms 

 a temporary prison for the small visitors. As they creep downwards on the 

 projecting, red-brown end of the spadix, they reach several rows of stiff bristles 

 situated close above one another at the top of the contraction in the spathe, 

 which stretch from the narrowed spadix to the inner surface of the spathe. The 

 midges creep through them in order to reach the warmth and the red-brown 

 colouring of the inner surface of the spathe, which from this point widens into 

 a pit. They cannot at once escape from this. The threads would not hinder their 

 creeping back through them, but 

 the insects try to fly out, and fail 

 to escape by this means, as they 

 are only struck back by the fence 

 of bristles when they fly towards 

 the bright upper part of the pit. 



The small prisoners find the 

 mature stigmas in the first stage 

 of anthesis, and deposit foreign 

 pollen upon them in the attempt 

 to gain the open once more. The 

 stigmas then shrivel up, and in 

 the place of each appears a minute 

 drop of nectar, as compensation 

 to the insects for their delay and 

 their work of pollination. The 

 anthers now dehisce and let their 

 pollen escape, so that it fills the 

 base of the pit, and the small 

 visitors are dusted with it. Mean- 

 while the bristles barring the en- 

 trance have become limp, and the 



spathe opened out, and the visitors can now leave their temporary prison without 

 difficulty. I have often observed that on cutting open a spathe the midges imme- 

 diately fly to another plant and again creep down into the trap. On leaving the 

 flower, therefore, they will go to another, and dust the stigmas with the foreign 

 pollen.^ 



Fig. 410. Aru7n maculatum, L. (after Herm. Miiller). 

 VI. External view of inflorescence. VII. Do., with the trap 

 cut open (xj). VIII. Do. (almost natural size). IX. Trans- 

 verse section just above the trap-hairs. a, Upper part of 

 spathe ; h, dark-purple tip of the spadix, serving as an attraction 

 and conducting-rod ; r, trap-hairs (vestigial stamens) ; d^ still 

 immature male flowers (anthers) ; f, vestigial female flowers 

 (ovaries), without any known function, possibly degenerate by 

 correlation of growth with the upper stamens ; f^ female flowers 

 (ovaries), in a receptive condition. 



' After completing my manuscript I have written as follows in the ' IlUist. Zs. fiir Entomologie,' 

 iii, 1878, p. 201 : — I had already found hundreds of specimens of Psychoda phalaenoides L. in the 

 trap of Arum maculatnm Z., at Iserlohn in Westphalia, and at Eutin. But in plants sent me on 

 June 8 of this year from the Castle Garden of Plon I have observed a larger number of these little 

 midges than I have previously seen. The traps were so full of them that free movement must have 

 been impossible, so closely were they packed together. In one trap there were no less than 6 cc. of 

 midges. These I spread out as evenly as possible on a surface of one sq. m., and counted those 

 occupying one sq. cm. as being forty on an average. There must, therefore, have been some 4000 

 midges in all within one trap. 



The extraordinary eagerness with which these midges visit the inflorescences of Arum is shown by 



