312 



PHY 



THE UNIVERSAL HERBAL; 



PHY 



most flowers have such a shape as would rather impede than 

 favour the access of .the wind. Koelreuter was the first who 

 observed clearly that many insects serve this purpose ; and 

 Mr. Sprengel had leisure and patience enough to examine in 

 the flower the manner in which insects proceed in completing 

 the impregnation of plants. He found that various species 

 of bees, as well as many of the flying insects, are selected 

 by nature for this purpose ; and lie even observed, that some 

 flowers had their peculiar insects, which alone visited them. 

 His observations on this subject are very numerous. Those 

 insects, it is true, do .not visit the flower_on purpose to 

 impregnate it, they only seek after the sweet juice which 

 exudes from it in the nectaries. Their hairy body, which 

 nature did not bestow without design, is covered with the 

 polleri, and, whenever they visit another flower of the same 

 species, the poDen is rubbed against the stigma, and impreg- 

 nation is the -consequence. And every insect that is not 

 limited to one sort of flower, but visits many indiscrimi- 

 nately, will, 'during a whole day, remain with the species on 

 which it first fixed in the -morning, and not touch another, 

 provided there be enough of the first species. Those flowers 

 on-ry w.hich secrete a sweet juice, -are visited by insects. 

 Several of these flowers have one or more coloured spots, 

 which Mr. Sprengel calls Macula indicantes, as they always 

 indicate that a .plant exudes honey, and, as he believes, 

 attracts them. In .flowers, the hairs are always placed so as 

 to prevent the rain from dropping in, and not to allow the 

 insect to enter the flower at that place, on purpose that it 

 may -be obliged to -make its way across the stamens. The 

 filiform and leaf-like appendages, which we enumerated 

 amongst the parts of flowers, and which defend the honey, 

 serve the same purpose. But it would be too prolix to give 

 a more detailed account of the manner in which insects do 

 ftiis, as any one has access to see and observe it, if in the 

 least acquainted with the structure of flowers. We need 

 only look -at the Iris igermanica, at many flowers of the class 

 Didynamia, at be Syrophytum afficinale, and many other 

 plants, in order to form a clear idea of it. One of the most 

 singular 'ways of the fecundation of plants through insects, 

 we have in the Aristolochia clematitis, which I shall decribe. 

 This flower has a linguiform corol, which at its inferior part 

 is spherical, towards the top it becomes long and tabular, 

 and its margins end in a flat and spear-pointed manner. 

 The pistil is placed in the round cavity of the corol, the 

 germen of which is surrounded by six anthers, which are 

 shorter than the germen itself. The germen has no style, 

 but is provided with a hexagonal stigma, which is very shal- 

 low, and on its upper surface has imbibing pores. The 

 anther -cannot empty the pollen upon the stigma, as the 

 flower stands always straight upright during the period of 

 flowering. The pollen therefore must necessarily fall to the 

 bottom of the flower without being used, if no insects come 

 near the flower. And indeed if it be tried, and all insects 

 kept from -the flower by a thin, but firmly closed piece of 

 gauze, no seeds will be formed. It happens indeed not 

 unfreqnently, that as it is a particular insect which impreg- 

 nates the flowers, when it is "wanting or not able to find the 

 flower, this last -withers without having a single seed. This 

 insect is the Tipula pennicornis. The round bottom of the 

 flower is, in its interior, quite smooth, but the tube is lined 

 with dense hairs, every one of which is turned towards the 

 interior, so as .'to form a kind of funnel, through which the 

 insect may very easily *nter, but as on its return all the 

 hairs oppose it, it cannot come out. Several insects creep in 

 through the aperture, but are obliged to remain in the cavity 

 of the corolla. Uneasy to fee corvfincd in so small a space, 



they creep constantly to and fro, and so deposit the pollen 

 on the stigma. After this is done, the flower sinks; the hair, 

 which obstructed the passage, shrinks and adheres closely to 

 the sides of the flower, by which means the small confined 

 gnats get free, and may now accomplish their farther destina- 

 tion. Who but must admire the wise provision of nature in 

 fecundating this seemingly trifling flower ! Other instances of 

 this kind could be mentioned. The dichogamic plants can 

 be no other way fecundated than by insects. Many flowers 

 blossom in succession on one plant, and the restless insect, 

 which flies from one flower to another, carries the polleti to 

 them all. -Epilobium angustifolium may serve as an instance 

 of male Dichogamy, and Euphorbia cyparissias as an 

 instance of female Dichogamy. Homogamic flowers, that is, 

 such flowers as have their male and female organs of gene- 

 ration formed at the same time, are mostly impregnated by 

 themselves. Several, however, are visited by insects, which 

 complete what perhaps was not completed in the usual "way, 

 or what rain, wind, or unfavourable weather, interrupted at 

 the proper period. In these flowers, the following arrange- 

 ment is made: When the stamens are larger than the pistil, 

 the flower stands upright, and the stamens incline themselves 

 over the pistil ; or it lies horizontally, and the stamens curve 

 themselves archways toward the style, so as to become of 

 the same length with the pistil. Of the first- kind, the Par- 

 nassia palustris is an instance. In it the stamens, five in 

 number, -recline all over the pistil in the following order: 

 First, one of the stamens places itself across the stigma, lets 

 its pollen go, then rises up and resumes its former position. 

 In the mean time the second is already following in the same 

 manner, and as soon as the first rises from the stigma, the 

 Other covers it ; the third succeeds like the two first, but as 

 soon as it has risen, the two last come both at once. To the 

 second kind belong the Horse Chesnut, (jEsculus hippocas- 

 tanum,) and others. But if in homogamic flowers the stamens 

 are shorter than the pistil, the flower is pendulous, so that 

 the pollen, when falling off, may be enabled to perform its 

 functions. Rarely have such flowers an oblique or horizontal 

 position, and in this case the style turns backwards, to reach 

 the stamens. Some pendulous flowers, however, can be 

 fecundated only by insects, as their stigma is so situated that 

 the pollen does not directly fall upon it ; but then these 

 flowers have, as mentioned before, hair or other processes, 

 which oblige the insect to enter them along the stigma ; so 

 that, when they return or visit the flower repeatedly, they 

 must rub the pollen against the stigma. Such plants as are 

 of different sexes, and on one stem have both female and male 

 flowers, are mostly impregnated by insects alone. Only 

 those impregnate themselves which have no nectaries, and 

 where the male flowers stand close to the female flowers, as 

 in some species of Gramina, Typha, Covx, Carex, and 

 others. In that case, such flowers have their female flowers 

 situated lower than the male flowers, and their petals are 

 very minutely or very deeply divided, so that the pollen, 

 when falling, can reach them. This is the case, for instance, 

 with the different species of Pimrs, and similar trees. Here 

 probably the wind too is of some -service. It disperses the 

 pollen in the air, so as often to involve the tree hi a kind of 

 cloud. The sulphur rain, as it has been 'called, whidh falls 

 sometimes in spring, after thunder storms, proceeds frbm the 

 pollen of the Pinus sylvestris. Such plants as have on one 

 Stem -male flowers only, on another female flowers alone, are 

 all provided with nectaries, and the 'male flowers are larger 

 and more obvious than the female, to allow more readily the 

 insects to carry the pollen to the female plant. The Valis- 

 neria spiraKs, a water-plant of Italy, is of different sexes ; 



