AUTOGAMY BY THE CLOSING OF THE COROLLA. 371 



margins of these lobes, and some of the pollen sticks to the petals, so that next day 

 when the flower opens again a streak of pollen may be seen along the middle line 

 of each of the outer petals (see fig. 304 ^). On the last day of bloom the two 

 stigmatic arms curve down, and when the flower closes once more at dusk, they, 

 being directed towards the median lines of the outer petals, are brought into contact 

 with the pollen adherent along those lines (see fig. 304^), and thus at the last 

 moment autogamy is efiected. 



The flowers of the Venus's Looking-glass (Specularia speculum, see figs. 

 30410,11,12,13,14,15^ are protandrous like those of the common Bell-flower (Cam- 

 panula); their anthers form a tube in the newly-opened flower (see figs. 304 ^^ and 

 304"), dehisce inwards and deposit the whole of their pollen on to the delicate hairs 

 which clothe the external surface of the stylar column. When the tube of anthers 

 breaks up through the shrivelling of their empty lobes, an axial column covered 

 with pollen is exposed to view, and is used by insects as an alighting place. For 

 the present pollen can only be taken away— not deposited — by insects, for the style- 

 arms are still united, and the receptive tissue is inaccessible. Every evening the 

 erect basin-shaped corolla folds up longitudinally in such a manner as to form five 

 re-entrant angles (see fig. 304 ^^). The in-folded angles of the corolla reach inwards 

 as far as the central column (see fig. 304 ^*), and get besmeared with some of the 

 pollen with which it is coated. The next morning when the corolla opens linear streaks 

 of poUen may be seen upon its internal surface. Meanwhile the three short arms 

 of the style have disunited and spread themselves out, whilst the pollen has fallen 

 oif the stylar column (see fig. 304 ^'), or been carried away by insects. If at this 

 stage insects alight on the divergent style-arms fresh from visiting younger flowers, 

 cross-pollination is certain to ensue. As night approaches the flower closes in the 

 same way as on the previous evenings, and the pollen sticking to the lines of the 

 internal folds comes against the style-arms, which are spread out and slightly 

 reflexed (see fig. 304^®), and thus effects self-pollination. In the event of the 

 stigmatic tissue having already received a deposit of foreign pollen, this act of self- 

 pollination is superfluous, but otherwise the process is eflectual, and always results 

 in the formation of fruit. A similar phenomenon may be observed in the nodding 

 or pendent flowers of various Solanacese, particularly in the Potato plant (Solanum 

 tuberosum), for here also there is frequently a transference of pollen to the corolla, 

 and from the folds of the corolla to the stigma. But in this case the pollen issues 

 from the anthers through terminal pores, and falls irregularly and not necessarily 

 upon particular parts of the corolla, so that autogamy is not so certain to take place 

 in these plants as in Specularia. 



From the above descriptions it will be seen that in Argemone, Hypecoum, and 

 Specularia, although the corolla is the part of the flower which is instrumental in 

 effecting autogamy, the process does not involve any noticeable elongation of the 

 pollen-besmeared corolla during the period of flowering. We have now to deal with 

 another group of plants in which the petals perform just the same function as in 

 the foregoing cases with respect to autogamy, but in which a very important part 



