370 AUTOGAMY. 



the pistil, and the stellate stigma, which offers the best alighting place for insects, 

 rests at a slightly higher level than the anthers, and at a sufficient horizontal dis- 

 tance from them to prevent their pollen from reaching, spontaneously, its receptive 

 tissue. In the course of the day insects arrive with pollen from other blossoms and 

 cause cross -pollination. When the evening comes the petals close up over the 

 pistil, an 1 one of them brings its inner surface, which is covered with pollen, into 

 direct contact with the stigma (see fig. 304 2 ). 



The case of the Hypecoum is far more complicated. The flowers of this plant 

 have two small sepals and four large tri-lobed petals (see figs. 304 3 and 304 *). The 

 latter are arranged in two pairs at right angles to one another, one pair being 

 inserted a little higher than the other. The middle lobe of each of the petals 

 belonging to the upper pair is curiously modified; its surface is concave, and in the 

 young flower has the shape of a spoon with fringed edges. The function of these 

 lobes is to collect all the pollen from the anthers at the very commencement of 

 flowering. The anthers are, like those of Composite, coherent into a tube inclosing 

 the style; but instead of opening inwards as the latter do, they are extrorse, i.e. 

 dehisce outwards. At the time of dehiscence and of the discharge of the pollen the 

 two spoon- or pouch-shaped central lobes of the upper petals are in close proximity 

 to the anthers, and they receive the whole of the pollen (see fig. 304 i ). After this 

 transfer has been accomplished the two lobes now containing the pollen separate 

 from one another, the first parts to disunite being the free extremities at the top, 

 then the lateral edges (see fig. 304 6 ). The pollen is thus exposed and may be 

 carried off by insects which come for the honey concealed in a little depression at 

 the base of each lobe (fig. 304 8 ). The two linear stigmas being in close contact 

 at this stage, their tissue is not as yet accessible; they do not disunite till two 

 days after the first opening of the flower, but when that interval has elapsed they 

 diverge, and then constitute the most convenient place for insects to settle upon. 

 They are now in exactly the same position as was previously occupied by the 

 pollen-laden lobes (see fig. 304 7 ), and therefore if an insect alights upon them after 

 visiting younger flowers, it is sure to dust the stigmatic tissue with foreign pollen. 

 Meantime the petal-lobes which received the pollen become much more reflexed, 

 especially at their lateral edges; the back of each lobe, which was originally convex, 

 is now deeply concave like a boat, and the whole structure is in a manner turned 

 inside out. The direction of the two divergent stigmas is at right angles to the two 

 upper petals, and their tips point towards the median line of the two outer ones. 

 In consequence of this arrangement the stigmas are at such a distance from the 

 pollen on the lobes that no autogamy could take place without some special inter- 

 vention. The requisite assistance is afforded by the two outer or inferior petals, 

 and their mode of action is as follows. When evening comes the flower closes ; the 

 two lateral pollen-free lobes of each superior petal rise up first of all, and then 

 the two inferior tri-lobed petals wrap themselves over them (see figs. 304 3 and 

 :io4 4 ). On the second or third day, when the margins of the pollen-laden lobes 

 have curled back, contact ensues between the two closed petals and the revolute 



