II AROIDEiE 391 



As, however, in Aristolochia, so also in Arum, small 

 flies, especially those belonging to the genus Psychoda, 

 attracted by the showy central spadix, the peculiar 

 smell, the prospect of honey, and perhaps of shelter, 

 enter the tube while the stigmas are mature, and find 

 themselves imprisoned by the fringe of hairs (Fig. 319, h), 

 which, while permitting their entrance, prevent them 

 from returning. After a while, however, the period of 

 maturity of the stigmas is over, and each secretes a 

 drop of honey, thus repaying the insects for their 

 captivity. The anthers then ripen and shed their 

 pollen, which falls on and adheres to the insects. Then 

 the hairs gradually shrivel up and set the insects free, 

 which carry the pollen with them, so that those which 

 then visit another plant can hardly fail to deposit some 

 of it on the stigmas. Often more than a hundred small 

 flies will be found, and in one case Knuth counted no 

 less than 4000 in a single Arum. 



Another explanation of the floral mechanism in Arum 

 maculatum has recently been suggested by Father 

 Gerard.^ He cousiders that the honey secreted by the 

 stigmas has a stupefying efiect on the insects, which are 

 killed and ultimately digested in the interior of the spathe. 

 The insectivorous habit is deduced from the presence 

 of dried remains of flies on the walls of the cavity. 

 Schnetzler ^ had previously claimed a similar insectivo- 

 rous habit for Arum crinitum. Self-pollination is not, 

 he thinks, precluded in A. maculatum,, some of the 

 stigmas being still functional when the anthers dehisce. 



The Aroids are mainly tropical. As regards the 

 leaves, see Dentaria (p. 80) and Petasites (p. 236). 



A. italicum appears to be the plant of our flora in 

 which the temperature relatively to that of the atmo- 

 sphere rises highest. The evolution of heat Avliich 

 accompanies the vigorous activity of vital processes 

 connected with flowering, was noticed in this species by 

 Lamarck, and quantitative experiments have been made 



^ Journ. Bot. August 1905. 

 ' Ann. and Mag. Nat. Hist. Ser. 5, iv. 1879, p. 399. 



