the long persistence of the corolla when fertilisation is prevented. I was informed, also, by a large horticulturist, that when the bees get at his flowers in the greenhouses the plants become almost worthless for sale, owing to the speedy fall of the blossom. The teleological significance of this is of course apparent. The corolla is of no further use when fertilisation has once occurred, and its maintenance is a useless burden. It is therefore cast off. But how this is brought about is not so obvious. I presume that the fertilisation causes a larger flow of nutriment to the stimulated ovary, and that this flow takes place at the expense of the corolla, which then perishes from starvation.

The last exceptions I shall consider are wild thyme (T. serpyllum) and marjoram (Origanum).

In each of these we have a didynamous flower, which certainly is fertilised by insects, for its anthers ripen and shed their pollen before the stigma is mature. The four anthers, however, are not placed longitudinally, one pair above the other, for the stamens diverge laterally and project beyond the corolla in a fan-shape. The breadth which the anthers thus cover is much greater than can come within the range of the centrally placed style. The difficulty, however, vanishes when, instead of examining a single flower, we consider the general mode of growth and the inflorescence. Thyme, as a rule, grows in patches. The small flowers are crowded together on the surface of the patch, forming a continuous carpet of blocm, from which project upwards the ripe anthers of the younger and the ripe stigmas of the older flowers. Over this carpet crawl the bees, their bodies so large in proportion to the individual blossoms as to be in contact with many at a time.

The crowded heads of marjoram form a similar carpet. Thus all parts of the under surface and sides of the bees get dusted with pollen, and similarly all parts come sooner or later into contact with stigmas. There is thus no occasion for that definite arrangement of the anthers which is profitable in the largeflowered didynamia. What is required is that the anthers should project beyond the corolla, and this they do.

It would clearly also be disadvantageous that the dehiscent surface of the anthers should be turned, as in most other didynamia, forwards. To ensure the readiest contact with the insect as it crawls over the flowers, this surface should face directly upwards. Now with the longer stamens, which are entirely free of the corolla, this is the case. The lower pair of anthers only, as a rule, half overtop the corolla's lip. The dehiscent side of their upper free lobe is turned upwards; that of the lower lobe faces forwards. Thus always the dehiscent surface assumes the most advantageous position. That of each free lobe is in

the position which brings it into contact with the bee as it crawls over the surface; that of the protected lobe is such that it will strike the bee's head as it sucks the nectar (fig. 8).

In most thyme plants the flowers are hermaphrodite. The stamens project from the corolla when the flower first opens; but it is only at a later period, when the pollen is in great part shed, that the style lengthens, and the stigma in its turn projects. This would seem to afford a tolerable security against self-fertilisation. Nature, however, seems bent on erecting a still stronger barrier, by entirely separating the two sexes. For a considerable proportion of thyme plants have flowers in which the stamens are abortive, and reduced to mere rudimentary points inside the tube, while the stigma projects when the flower first opens.* There are thus thyme plants which bear only female flowers. Whether there are also others which bear only male flowers, I cannot say. I have, however, never found such an one. All that I have been able to make out is that very frequently in the hermaphrodite flowers the stigma fails to arrive at maturity. It seems hardly too rash to foretell that in the course of time these hermaphrodite flowers will cease altogether to possess stigmas, and that thyme will be purely diœcious.

Still more surely may it be foretold of another plant-the horsechestnut-that in time it will be purely monoecious. If one of its pyramidal flower spikes be examined, the greater number of the flowers will be found to have the following structure. A sweet fluid is secreted at the base of the corolla, and access is open to this just under the two upper petals, on each of which is a dab of bright colour, while the rest of the corolla is white. The stamens are so curved and the anthers so set that a bee cannot get at the nectary without smearing its under surface with pollen. In the midst of the stamens a small pistil will be seen, which never developes to maturity, so that these flowers are in fact male flowers. Some few flowers, on the other hand, will be found in the spike, and almost always in the lower part, in which the style and stigma are fully developed, and have just the same curved form and position as above belong to the stamens and anthers. In these pistillate flowers there are also stamens; but these are not turned towards the entrance to the nectary. Their anthers, moreover, as a rule, fall off without dehiscing, although there is pollen to be found on section within their lobes. These lower flowers, then, are practically female flowers, and their stigmas will strike

The flowers in which the stamens are rudimentary have also a much shorter tube than have the ordinary ones, so short that the lower lip is in contact with and supported by the two anterior long teeth of the calyx.

the same part of a bee which above would be struck by the anthers.

Besides these male and these female flowers, others will be found--usually intermediate in position-which appear to be fairly hermaphrodite. In these not only do the anthers ripen their pollen, but the pistil, though it is not nearly so large as in the purely female flowers below, yet matures and is often fertilised. It is not without its use that the flowers which are becoming male should be at the apex, and those which are becoming female should be at the base of the spike; for thus any pollen which is shaken out by the wind will have a better chance of being utilised than were the positions reversed, as in poterium.

A word as to the dabs of bright colour on the upper petals. It is so excessively common to find such ornaments about the entrance into the nectary of flowers that one can hardly help suspecting that their position in that part serves some useful purpose. May it not be that the colour acts as a guide to the insect, attracting and directing it to the proper entrance? The marvellous ease and rapidity with which insects find their way to the nectary would thus in part be explained. A fact given by Mr. Darwin, as a striking case of correlation, seems to me strongly in favour of the explanation I have advanced. "I have recently observed," says Mr. Darwin, " in some garden pelargoniums that the central flower of the truss often loses the patches of darker colour in the two upper petals, and that when this occurs the adherent nectary is quite aborted; when the colour is absent from only one of the two upper petals, the nectary is only much shortened." *

66

I should say that in pelargonium, as in a host of other flowers, the anthers shed their pollen before the stigma is mature; and that anthers and stigmas turn when mature upwards, so that a bee, in getting to the nectary, rubs them with the under surface of its body, and thus carries the pollen of the younger flowers to the stigma of the more advanced

ones.

EXPLANATION OF PLATE LVI.

FIG. 1. Pedicularis sylv. Longitudinal section, (a) point, which probably protects the stigma during egress of bee; (b) anterior filament, with hairs on its upper part where it passes under the lower anther (f) to terminate in the (e) upper one; (c) posterior filament, without hairs on the upper part; (d) style; (e and f) upper and lower anthers. The cells are open and face the spectator.

* "Origin of Species," p. 145.

FIG. 2. Melampyrum pratense. Longitudinal section, (a) ring of glandular hairs; (b) filament of anterior stamen, on which the bee presses laterally; (c) posterior filament.

FIG. 3.

Teucrium scorodonia. Just expanded. The anthers full of pol-
len, dehiscent in front, and anterior to the style.

FIG. 4. Teuc. scor. At a later period. The anthers empty, thrown back
with the filaments; the style inclined forwards.
Digitalis purp. All the anther lobes horizontal and not yet open.
Digitalis purp. The upper anthers with their lobes vertical and

FIG. 5.
FIG. 6.
FIG. 7.

dehiscent. Digitalis purp.

lobes.

The lower anthers still horizontal.

The lower anthers also with vertical dehiscent

FIG. 8. Origanum vulgare. The style yet immature.

FIG. 9. Gesneria sp.? (a) Just open and with anther disk in front of the stigma; (d) anther disk. (6) Later stage-anther disk (d) against anterior wall.

FIG. 10. Gesneria sp.? Seen from front, a piece of the corolla having been removed; (d) anther disk in front of stigma; (e) style, the stigma hidden by the disk.

57

ON SOME INTERESTING POINTS IN THE HISTORY OF THE POLYZOA.

BY THE REV. THOMAS HINCKS, B.A. ¦

THE

HE Polyzoa have recently engaged the attention of many excellent observers and physiologists, and the result has been that much new light has been thrown on their history. The members of the class offer many attractions, both to the collector and the philosophic zoologist, and accordingly they have been diligently sought for and earnestly studied. The number of known forms has been largely increased, and a corresponding advance has been made in the knowledge of their structure and development. But whilst we have been steadily attaining a more accurate conception of what they are, we seem to be as far removed as ever from any general agreement as to what they should be called. Continental Europe pertinaciously insists on giving them Ehrenberg's name, Bryozoa; England and America are equally unanimous and resolute in their adhesion to J. V. Thompson's very happy designation, Polyzoa. It is in all ways desirable that scientific nomenclature should be uniform and cosmopolitan, and it must be accounted a scandal that France, Germany, and England cannot agree upon a name for this important group. If the subject were referred, in the fashion of the day, to a conference, which might take place at the meeting of our own British Association, or of one of the kindred societies on the Continent, it might be possible to get rid of a diversity of usage which represents no scientific principle and has no special significance whatever.

The Polyzoa have had their vicissitudes of fortune amidst the revolutions which have swept over zoological science. time when external resemblances had more weight with the classifier than the details of organisation, they ranked with the zoophytes. An increasing knowledge of their structure gradually detached them from their Coelenterate companions, and they appeared first as Molluscan Zoophytes, and then as Molluscoida, at the base of the great Molluscan series. In Professor Huxley's latest work on classification they are raised, in combination with