PHYSIOLOGY OF THE FLOWER. 125 



A bunch of primroses, 1 examined with a little care, will show 

 that the flowers are of two kinds {dimorphic) — (1.) long-styled, 

 with the stigma in the throat of the corolla tube, and anthers 

 deep down in it; (2.) short-styled, with these positions reversed. 

 Imagine now, in a long-styled flower, an insect alighting on the 

 convenient platform afforded by the salver-shaped corolla, and 

 inserting its trunk into the tube to get nectar. A particular 

 part of the trunk will be dusted with pollen, and, if a short- styled 

 flower is next visited, that part will touch the correspondingly 

 placed stigma. A new part will also be dusted, with similar 

 result. Moreover, the pollen from a short-styled flower is made 

 up of larger grains, since the pollen tubes are destined to reach a 

 greater length. 



Purple loosestrife is trimorphic, i.e., possesses three kinds of 

 flowers, each of which has a style of certain length, and two sets 

 of stamens different from the style and from another in that 

 respect. Thus there are the following three sorts of flower : — 

 (1,) Long-styled, with medium and short stamens; (2.) medium- 

 styled, with long and short stamens ; (3.) short-styled, with long 

 and short stamens. A little consideration will show that pollen 

 from a stamen of particular length will be carried to the stigma 

 of a style of the same length. The best effect will be thus pro- 

 duced, but other combinations are not excluded. 



Although the wild arum (fig. 33) has no perianth, yet it is 

 degraded from a condition when a regular one was present, and 

 so may be considered here. The inflorescence has already been 

 described (p. 76). The aborted upper male flowers form a circlet 

 of threads radiating downwards and touching the spathe. Small 

 insects, attracted by the bright axis, can enter, but are not able 

 to get out again. The female flowers are first matured, and 

 some of the insects are likely to carry in pollen for their benefit. 2 

 After pollination they excrete nectar, no doubt to the great joy 

 of the hungry captives, which remain in durance, however, till 

 the pollen is shed, when they, all dusty, are freed by withering 

 of the chevaux-de-frise. Gladly they sally forth, and perchance 

 falling into a like prison, brush their coats against a new lot of 

 stigmas. 



A pretty arrangement for preventing self-pollination is found 

 in iris. This presents three admirable landing-stages for bees 

 in its reflexed petaloid sepals. Facing the alighting insect is a 

 stamen with outwardly dehiscing anther, arching over which is 

 a little shelf borne by a petaloid style. The stigmatic upper side 

 of this shelf is likely to be pollinated as the insect settles. The 



1 Chinese primrose, cowslip, oxlip, or polyanthus will serve equally well. 



2 As many as a hundred small insects have been found imprisoned. 



