In most plants the reproductive function inheres in a single bisexual flower, consisting of both male and female elements. In walnuts, as well as most other nuts, the male and female functions are performed by unisexual flowers of very different type and appearance. Both the male or staminate flower and the female or pistillate flower spring from buds that are formed in the axils at the base of leaves of the previous season's growth. In the Persian walnut they may be detected as early as July. The staminate bud that forms the pollen-producing catkin of the next season, can be distinguished by its checkered appearance, something like a tiny pine cone. They occur in the axils of the lower leaves of the shoot of the current season. The pistillate bud, which produces the nut, occurs at or near the tip of the growth of the current season. It can usually be distinguished from leaf buds by its larger size and plumpness. When these blossom buds develop the following season, the male or staminate blossom assumes the form of a catkin, which elongates rapidly a few days before maturity. As the pollen is shed, beginning at the stem end, the pale yellow-green of the bursted pollen capsule turns dark or black, proceeding to the tip of the catkin. This change readily shows that pollen is shedding, which may be confirmed by touching such a catkin with the tip of the finger, and noting the yellow pollen that adheres, or rises in a tiny cloud. Making note of the date when a given variety begins shedding pollen, and the date when all catkins on the tree have opened, gives the period during which that variety is effective as a pollinizer. The female, or pistillate flower, does not, like the catkin, spring directly from the wood of last season's growth, but occurs at the end of the new growth of the current year, being preceded by a number of leaves which nourish the young nut to maturity. The pistillate blossom assumes the form of one or more tiny nutlets with little sharp-pointed tips. When the blossom has become receptive to pollen, each tip has separated into two separate pistils which spread apart and present fresh, slightly sticky surfaces, which are known as stigmas. This is the time that pollination can take place, which period continues until the stigmas have lost their freshness and stickiness. This period marks the time during which pollination can occur.