PHYSIOLOGY OF THE FLOWER. 125 
A bunch of primroses,! 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 Jarger grains, since the pollen tubes are destined to reach a 
greater length. 
Purple loosestrife is trimorphic, t.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.) mediwm- 
styled, with long and short stamens; (3.) short-styled, with long 
and medium 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 produced, 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 reduced 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.? 
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 set 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. 
? As many as a hundred small insects have been found imprisoned. 
