Fig. 197.—Fruit of St. Valery apple cut lengthwise.
Pleiotaxy of the gynœcium.—An increase in the number of whorls of which the pistil consists is not of very frequent occurrence. Generally after the formation of the whorl of carpels, the energy of the growing point ceases, or if by chance it be continued, the result is more generally the production of a new flower-bud (median prolification) than the repetition of the carpellary series. It is necessary also to distinguish between the veritable augmentation of the pistil and the semblance of it, brought about by the substitution of carpels for some other organs, as pistillody of the stamens, and even of the segments of the perianth, is not very unfrequent, as has already been stated under the head of substitution. Again, the increased number of carpels which is sometimes met with in such flowers, as Magnolia or Delphinium, where the ovaries are arranged in spiral series, is not strictly referable to the present category.
The orange is one of the plants most frequently subject to an augmentation in the number of carpellary whorls; sometimes this is due to the stamens assuming the guise of carpels, but at other times the increase occurs without any alteration in the stamens or other organs. If the adventitious carpels be exposed, they are covered with yellow rind, while those portions that are covered by the primary carpels are destitute of rind. Some varieties of the double tulip are very subject to a similar change, but, in this case, the petals and the stamens very frequently become more or less carpellary in their nature. Fig. 196 represents an increased number of whorls of carpels in the variety called "rex rubrorum," the segments of the perianth having been removed.
In the St. Valery apple, already referred to, there is a second whorl of carpels above the first, a fact which has been made use of to explain the similar structure of the pomegranate.
The tomato (Lycopersicum esculentum) is another plant in which an adventitious series is frequently produced, and generally in combination with the primary series.
In the Chinese primrose (Primula sinensis) a supernumerary whorl is frequently met with, generally associated with other changes in the construction and arrangement of the parts of the flower.
M. de Candolle[455] mentions a flower of Gentiana purpurea with four carpels in one series, and five others in the circle immediately above them. Wigand[456] alludes to an instance wherein there was a second pair of carpels above the first in Vinca herbacea. Dr. Sankey has forwarded flowers of a Pelargonium having a double series of carpels, eight in the outer row, five in the inner, and this condition is stated to exist in the flowers of the same plant for two years consecutively. In Aquilegia I have met with a similar increase in the whorls of carpels.[457] Meissner records a similar augmentation in Polygonum orientale.[458]
Wigand[459] describes and figures a flower of Vinca minor, in which there were two carpels intervening between the ordinary pair, and a similar illustration has been observed by the writer in Allamanda cathartica. Eichler[460] has put on record a similar case in a capparid.
Marchand[461] mentions a polycarpellary berberid (Epimedium Musschianum). The supernumerary carpels in this flower were placed on a short axis, which originated in the axils of the stamens, and as these latter organs were present in their usual number and position, the adventitious carpels could not be considered as resulting from a transformation, or substitution of carpels for stamens.