[327.] A Disk is an enlarged low receptacle or an outgrowth from it, hypogynous when underneath the pistil, as in Rue and the Orange (Fig. [363]), and perigynous when adnate to calyx-tube (as in Buckthorn, Fig. [364, 365]), and Cherry (Fig. [271]), or to both calyx-tube and ovary, as in Hawthorn (Fig. [273]). A flattened hypogynous disk, underlying the ovary or ovaries, and from which they fall away at maturity, is sometimes called a Gynobase, as in the Rue family. In some Borragineous flowers, such as Houndstongue, the gynobase runs up in the centre between the carpels into a carpophore. The so-called epigynous disk (or Stylopodium) crowning the summit of the ovary in flowers of Umbelliferæ, etc., cannot be said to belong to the receptacle.
Fig. 364. Flower of a Buckthorn showing a conspicuous perigynous disk.
Fig. 365. Vertical section of same flower.
Section XIII. FERTILIZATION.
328. The end of the flower is attained when the ovules become seeds. A flower remains for a certain time (longer or shorter according to the species) in anthesis, that is, in the proper state for the fulfilment of this end. During anthesis, the ovules have to be fertilized by the pollen; or at least some pollen has to reach the stigma, or in gymnospermy the ovule itself, and to set up the peculiar growth upon its moist and permeable tissue, which has for result the production of an embryo in the ovules. By this the ovules are said to be fertilized. The first step is pollination, or, so to say, the sowing of the proper pollen upon the stigma, where it is to germinate.
[§ 1.] ADAPTATIONS FOR POLLINATION OF THE STIGMA.
329. These various and ever-interesting adaptations and processes are illustrated in the "Botanical Text Book, Structural Botany," chap. VI. sect. iv., also in a brief and simple way in "Botany for Young People, How Plants Behave." So mere outlines only are given here.