Word Finder - micropyle

definition

In seed-bearing plants, a small opening in the integuments of the ovule through which sperm are able to access the ovum.

definition

The hilum of an ovum at the point of attachment to the ovary; any opening in the coverings of an ovum by which spermatozoa may find entrance.

There are five, or sometimes fewer, carpels, which unite to form an ovary with as many chambers, in each of which are one or two, rarely more, pendulous anatropous ovules, attached to the central column in such a way that the micropyle points outwards and the raphe is turned towards the placenta.

The development of the ovule, which represents the embryo- Gymnosperms; when mature it consists of one or two sac. coats surrounding the central nucellus, except at the apex where an opening, the micropyle, is left.

In Casuarina, Juglans and the order Corylaceae, the pollen-tube does not enter by means of the micropyle, but passing down the ovary wall and through the placenta, enters at the chalazal end of the ovule.

Such a method of entrance is styled chalazogamic, in contrast to the porogamic or ordinary method of approach by means of the micropyle.

In some Monocotyledons, Pistil and macrosporangium, is very similar to the process in Fertiliza- to the opening of the micropyle, into which the pollen- tion.

Brown's views as to the structure of the unimpregnated ovule (with the introduction of the term "sac embryonnaire"); and in that it shows how nearly Brongniart anticipated Amici's subsequent (1846) discovery of the entrance of the pollen-tube into the micropyle, fertilizing the female cell which then develops into the embryo.

The ovary is small, rounded to elliptical, and one-celled, and contains a single slightly bent ovule sessile on the ventral suture (that is, springing from the back of the ovary); the micropyle points downwards.

A young ovule consists of a conical nucellus surrounded by a single integument terminating as a two-lipped micropyle.

In Araucaria and Saxegothaea the nucellus itself projects beyond the open micropyle and receives the pollen-grains direct.

The female flower is enveloped in a closely fitting sac-like investment, which must be regarded as a perianth; within this is an orthotropous ovule surrounded by a single integument prolonged upwards as a beak-like micropyle.

A complete and functional female flower consists of a single ovule with two integuments, the inner of which is prolonged into a narrow tubular micropyle, like that in the flower of Gnetum.

The micropyle m is very wide.

The integuments do not completely invest the apex of the nucellus, but an opening termed the micropyle is left.

The micropyle indicates the organic apex of the ovule.

This embryo-sac increases in size, gradually supplanting the cellular tissue of the nucellus until it is surrounded only by a thin layer of it; or it may actually extend at the apex beyond it, as in Phaseolus and Alsine media; or it may pass into the micropyle, as in Santalum.

When the ovule is so developed that the chalaza is at the hilum (next the placenta), and the micropyle is at the opposite extremity, there being a short funicle, the ovule is orthotropous.

The ovule is curved upon itself, so that the micropyle is near the funicle.

In angiosperms when the pollentube reaches the micropyle it passes down into the canal, and this portion of it increases considerably in size.

The neck of the flask-shaped pollen-chamber projected a little from the micropyle and no doubt received the pollen directly.

This is a large seed, with a very long micropyle; it has a beaked pollen-chamber, and a complex integument made up of hard and fleshy layers, closely resembling the seed of a modern Cycad; the nucellus, however, was free from the integument, each a sketch after Kidston.

Upper part of seed, in longitudinal section; i, integument; mi, micropyle; n, remains of nucellus; p.c, pollen-chamber (containing pollen-grains), with its canal extending up to the micropyle; pr, part of prothallus; ar, archegonia.