DISPERSION OF POLLEN BY ANIMALS. 165 



become flaccid, midges that have been imprisoned at the bottom of the cavity pass 

 into the upper story, they are kept there for a time by the upper bristles, which 

 are still rigid, so that the insects knock against the male flowers and must cover 

 themselves with pollen. Finally, when this object is achieved, the upper bristles 

 also relax and the midges are allowed to escape. 



It is astonishing what a large number of insects and what a variety of different 

 kinds find a home in the flowers of Aroidese. The smaller Aroids, such as Arum 

 maculatum, widely distributed in Europe, are sought chiefly by tiny midges of the 

 species Psychoda phallcenoides, and it is not uncommon to find several hundreds 

 of them in the cavity of a single spathe. In the receptacle formed by the spathe of 

 an Arum conocephaloides, planted in the Botanic Gardens of Vienna, three species 

 of small black midges of the genus Ceratopogon had congregated, and were present 

 in such large numbers that when one of the spathes was opened artificially a whole 

 swarm flew out. A second spathe of the same plant, which was immersed in alcohol 

 and subsequently opened, was found to contain nearly a thousand midges of the kind. 

 In the Italian Arum (Arum, Italicum) also as many as sixteen different species 

 of flies, mostly of the genera Ghironomus, Limosina, Sciara, and Psychoda, have 

 been found in a single spathe. Another Aroid, Bracunculus crinitus, is sought 

 principally by large flies belonging to the species named Somom,yia Caesar and 

 Anthomyia scalaris. In the receptacles formed by the spathes of the Bracunculus 

 Greticus, which has flowered in the Botanic Gardens of Vienna, various carrion- 

 beetles (Aleochara fuscipes, Bermestes undulatus, Saprinus nitidulus. Sac.) had 

 collected, besides numerous green-gilded flies of the genera Anthomyia, Lucilia, 

 and SoTnomyia; and in the sheathing-bracts of Bracunculus vulgaris which grows 

 in Italy scarcely anything but carrion-beetles of the genera Bermestes and Saprinus 

 have been observed. A single spathe of the last-named plant was once found to 

 contain more than 250 carrion-beetles belonging to eleven different species. 



The flowers of the Birthwort genus (Aristolochia) bear a surprising resemblance 

 to the spathes of Aroideee, their perianths being, like aroid spathes, divided into three 

 regions. First of all, there is the limb, which in the European species has the form 

 of a trumpet, and in the tropical species of America assumes many other curious 

 shapes, as, for instance, that exhibited by Aristolochia ringens (fig. 242), where it 

 is drawn out into a boat-shaped under-lip with an upper-lip arching over it. Next 

 comes a tubular median portion, which is furnished with various contrivances to 

 prevent the egress whilst permitting the entrance of creatures seeking shelter. 

 Lastly, there is an enlarged basal portion like a bladder or pouch wherein the 

 stigma and anthers are situated, and which constitutes the goal of the insect- visitors. 

 On a future occasion it will be necessary to enter more fully into the manner in 

 which the insects that creep into the pouch take up and afterwards deposit the 

 pollen, and it will therefore be suflScient to mention here that they are kept pri- 

 soners there until the anthers have opened. When dehiscence has taken place, and 

 not before, the tubular middle region undergoes certain changes which make it 

 possible for the captives to escape from their temporary dungeon. 



