Better seeds--that is, those that produce stronger and more fruitful plants--often result when the _pollen comes from another flower_. Fertilization effected between different flowers is =cross-fertilization=; that resulting from the application of pollen to pistils in the same flower is =close-fertilization= or =self-fertilization=. It will be seen that the =cross-fertilization= relationship may be of many degrees--between two flowers in the same cluster, between those in different clusters on the same branch, between those on different plants. Usually fertilization takes place only between plants of the same species or kind. [Illustration: FIG. 195.--DIAGRAM TO REPRESENT FERTILIZATION. _s_, stigma; _st_, style; _ov_, ovary; _o_, ovule; _p_, pollen-grain; _pt_, pollen-tube; _e_, egg-cell; _m_, micropyle.] In many cases there is, in effect, _an apparent selection of pollen_ when pollen from two or more sources is applied to the stigma. Sometimes the foreign pollen, if from the same kind of plant, grows, and fertilization results, while pollen from the same flower is less promptly effective. If, however, no foreign pollen is present, the pollen from the same flower may finally serve the same purpose. In order that the pollen may grow, _the stigma must be ripe_. At this stage the stigma is usually moist and sometimes sticky. A ripe stigma is said to be =receptive=. The stigma may remain receptive for several hours or even days, depending on the kind of plant, the weather, and how soon pollen is received. Watch a certain flower every day to see the anther locules open and the stigma ripen. When fertilization takes place, the stigma dies. Observe, also, how soon the petals wither after the stigma has received pollen. =Pollination.=--The transfer of the pollen from anther to stigma is known as =pollination=. The pollen may fall of its own weight on the adjacent stigma, or it may be carried from flower to flower by wind, insects, or other agents. There may be =self-pollination= or =cross-pollination=, and of course it must always precede fertilization. Usually the pollen is discharged by the bursting of the anthers. The commonest method of discharge is through a _slit_ on either side of the anther (Fig. 193). Sometimes it discharges through a _pore_ at the apex, as in azalea (Fig. 196), rhododendron, huckleberry, wintergreen. In some plants a part of the anther wall raises or falls as a _lid_, as in barberry (Fig. 197), blue cohosh, May apple. The opening of an anther (as also of a seed-pod) is known as =dehiscence= (_de_, from; _hisco_, to gape). When an anther or seed pod opens, it is said to _dehisce_. [Illustration: FIG. 196.--ANTHER OF AZALEA, opening by terminal pores.] [Illustration: FIG. 197.--BARBERRY STAMEN, with anther opening by lids.]