On the Flowers of Aralia Spinosa L., and Hedera Helix L.
By THOMAS MEEHAN.
The study of Aralia spinosa, L., affords some interesting facts which do not seem to have attracted the attention of other observers.
In Dr. Gray's indispensable Manual of Botany, it is said to be "more or less polygamous." I have had many specimens under my daily observation this season, from the earliest opening till the last blossom appeared, and find that it is much more nearly monoecious than the above quotation would imply.
There are three different sets of flowers corresponding to the thrice compound branchlets of the large panicle. When the flower scape elongates, it seems suddenly arrested at a given point, and a very strong umbel of female flowers appears at the apex. A great number of secondary branches appear along this main one; and they also suddenly terminate each with an umbel of female flowers. From these secondary branches a third series appear, and these flowers are well filled with anthers that are abundantly polleniferous. The female organs of these flowers of the third class, are, however, defective, as only a few bear capsules, and in these a large portion of the seeds have no ovules. The polygamous character is confined to this third series of flower, the first two having purely pistillate blossoms. In these there do not seem to be the rudiments of stamens.
The most remarkable part of this process of development is, that the whole of this first series of female flowers should open so long before the male ones come, that they fall unfertilized. Most part of the second series also fall, and the crops of seeds is mainly made up of a few of the last opening ones of the section, and the comparatively few hermaphrodite ones which are found in those of the third class. It is a matter for curious speculation what special benefit it can be to the plant to spend so much force on the production of female flowers too early to mature, and then producing such an immense mass of pollen to go utterly to waste.
It may not be amiss to note, that in the common carrot the earlier strong umbels have often a male flower in the centre; and that while the usual flowers are of a pure white, this one is a crimson color. In the central umbels of Aralia spinosa, and at times on spurs along the branchlets of the panicle are similar colored processes, so small that their form cannot be made out by a common pocket lens. Our fellow member, Dr. J. Gibbons Runt, makes them out, under the dissecting microscope, to be vase-like forms with five minute reflexed segments, and with a small solid disk in the centre. It is interesting as evidently being a successful attempt of an abortive flower to simulate in some respects a real one of another character.
Examining, also, the flowers of the allied European Evergreen Ivy, Hedera Helix, L., I find similar laws of distribution of the sexes as in Aralia spinosa, with the addition of a somewhat different structure in the male from the female flowers.
In Europe the plant is described as often having a single umbel as a flower spike. It is quite likely in these cases the flowers are hermaphrodite. In all the cases I have met here, the inflorescence is a compound of several umbels,—a terminal one—female, and the lateral ones male, as in Aralia. But there are rudiments of stamens in the flower, and in occasional instances I find a filament developed; but never, so far, with any polleniferous anthers. The flowers of the central female umbel have rather longer and stronger pedicles than the lateral male ones. The calyx is united with the ovarium for one-half its length, and the latter much developed in the unopened flower. In the male the segments of the calyx are two-thirds free, and the petals are much longer than in the female flowers.
As in Aralia spinosa, the male flowers do not open until some time after the female ones; and not before some of the latter, impatient of delay, have fallen unfertilized.
I have so often and in so many ways demonstrated to the Academy that in plants the male element is a latter and inferior creation, that it seems almost superogatory to point out that these plants illustrate the same principle. But it is a part of the record of what I believe to be unobserved facts in relation to these species, therefore I briefly allude to them.—Proc. Acad. Nat. Sci., No. 3, 1870.