402 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



and fruiting obviously cannot occur. It is instances of this kind that are adduced 

 by the older botanical writers to prove that the hermaphrodite flowers of certain 

 species are infertile. 



Plants have also been regarded as sterile from the fact that the particular 

 insects necessary for the transfer of their pollen were absent from the locality in 

 which the observations were made. Thus, Paederota Ageria, a plant not infre- 

 quently found in rocky crannies in the Southern Alps, and cultivated in large quan- 

 tity in the Innsbruck Botanic Garden, was always found to be sterile in the last- 

 mentioned locality, although it flowered profusely. The flowers of the plant require 

 insects to pollinate them, as the relations of the parts are such that autogamy can- 

 not occur. Since the particular insects which visit it in its own habitat are absent 

 from the Botanic Garden, the plant is infertile from lack of pollination. In its own 

 home in the Southern Tyrol and Krain, where these insects are present, it ripens 

 an abundance of fruits. The same is the case with several introduced plants which 

 have become partially wild. The Sweet Flag (Acorus Calamus), truly indigenous 

 to Eastern Asia, has spadices of densely-crowded, hermaphrodite flowers. The indi- 

 vidual flowers are strongly protogynous, and when the anthers open, the stigmas 

 of the same flower are already faded. Autogamy is consequently excluded. The 

 opening of the flowers is from below upwards, and when the anthers of the lowest 

 flowers are discharging their pollen the stigmas of the uppermost flowers are still 

 capable of pollination. Could the pollen pass from the lower to the upper flowers, 

 geitonogamy would take place, but this is only possible through the agency of 

 insects, as the pollen is adhesive. In Europe, where the plant is not originally 

 indigenous, this never happens, as the insects which visit it are absent; consequently, 

 with us, Acorus is always sterile. But further east, where it is indigenous, its 

 flowers are pollinated by insects, and it produces its fruit in spikes of red berries. 

 The Day Lily (Hemerocallis fulva) has ephemeral flowers which open in the morning 

 in summer-time between 6 and 7 o'clock, and close between 8 and 9 in the evening. 

 Its flowers are protogynous for a very short time. For half an hour before the 

 opening of the flower the mature stigma projects from the tip of the perianth. 

 Simultaneously with the folding back of the perianth, the anthers liberate their 

 adhesive pollen. The style being longer than the stamens, its stigma is not auto- 

 matically pollinated. For pollination insect visits are necessary. Honey is secreted 

 at the base of the tube of the perianth, which is 2 cm. long. The entrance to this 

 honey is so narrow that only a very delicate proboscis can gain access. Beetles, 

 flies, bees, and other short-tongued insects cannot get it, nor would they be of any 

 use for pollination if they could. The whole flower seems adapted for the visits of 

 some large butterfly with a long, thin proboscis, but curiously enough the flowers of 

 Hemerocallis fulva are never visited by butterflies in Europe. As autogamy is 

 excluded, the flowers remain unpollinated, and are sterile. Neither in gardens, 

 where it is much cultivated, nor in its semi- wild state does the Day Lily ever fruit 

 with us. It is more than probable that ffemerocallis is visited, in Northern Asia 

 and Japan, where it is truly indigenous, by some butterfly absent from Europe. 



