m 



244 TAKING UP OF POLLEN BY INSECTS. 



ferae, Dipsacese, and Caryophyllacese, which, owing to the association of large 

 numbers of flowers in umbels, fascicles, spikes, or capitula, afford a playground 

 richly furnished with slender waving stamens where pollen is easily to be shaken 

 or brushed off the anthers on every hand, although each single blossom only con- 

 tains a few stamens. In the case, too, of the single flowers of Roses, Anemones, 

 Peonies, Poppies, Magnolias and Opuntias, which are well supplied with stamens, 

 insects pushing between the anthers or feasting on pollen that has dropped upon 

 the petals get covered on head, thorax, abdomen, wings, and legs with the floury 

 pollen. This is true also of the spathes of Aroideae and of fig-inflorescences which 

 are haunted by midges, beetles, and gall-wasps, and deposit their pollen on these 

 visitors as they crawl out of their temporary refuge in the manner described on 

 pages 156-160. Mention was made in the same chapter of the fact that insects, 

 after being imprisoned for a time in the flowers of the Aristolochia, are quite 

 covered with pollen when they emerge. The phenomenon, which was there merely 

 glanced at, is so remarkable that it is worth while to give a somewhat fuller account 

 of it. In the widely-distributed species of Birthwort represented in fig. 257 ^ on 

 p. 226, and named Aristolochia Clematitis, the way into the enlarged base of the 

 flower is over a convenient ligulate alighting-place and through a dark and com- 

 paratively narrow passage lined with hairs. The free extremities of these hairs 

 point inwards, i.e. towards the inflated chamber, and they permit visitors from the 

 insect-world — small Black midges of the genera Ceratopogon and Ghironomus — to 

 pass into the chamber. But once inside, the midges are obliged to reconcile them- 

 selves to remaining imprisoned for a couple of days. The hairs, whilst ofiering no 

 hindrance to ingress present a bristling stockade of points to insects seeking to 

 escape (see fig. 257 % At first the midges endure their captivity with complacence, 

 for the warmth of their dungeon suits them, whilst the succulent cells lining its walls 

 afibrd a certain amount of nutriment. On the second or third day of imprisonment 

 the lateral walls of the anthers, which are adnate to the stigmatie column, open and 

 let the mealy pollen fall to the bottom of the chamber. The pollen is also acceptable 

 to the midges for food, and they feast upon it liberally. At last, however, they 

 become restless and look for a means of exit, and in bustling actively about the 

 chamber, they cover their entire bodies with pollen. After this the hour of their 

 deliverance is no longer deferred. The hairs in the narrow passage wither and 

 coUapse, leaving a free exit, and the midges all be-powdered with pollen hasten to 

 leave the flowers. That they retain no unpleasant recollection of their temporary 

 confinement may be inferred from the fact that they have no sooner escaped from 

 one flower than they creep into another, which has only just reached the stage at 

 which entrance becomes possible. This latter circumstance must be emphasized in 

 order to arrive at a complete understanding of the significance of the curious pheno- 

 menon just described. The moment the flower is accessible to insects, the stigma 

 is ready to receive the pollen whilst the anthers are still closed. When the midges 

 proceed from an older to a younger flower, they brush against the latter's stigma, 

 which IS situated right in front of the inner end of the dark passage, and deposit 



