2. Nuts.—Examine a hazel nut. Notice the sheathing bracts at the base of the fruit. Crack the nut and examine the broken edge of the shell (pericarp) with a lens. Make out the three layers which compose it. How many seeds are present? Cut the seed (kernel) across and see that the bulk of it consists of two cotyledons (Chap. I.). Does the fruit open of itself, if undisturbed? Compare the acorn of the oak. Trace the development of the acorn from the female flower, noticing that the cup is developed from a wrinkled disc surrounding the lower part of the flower. Cut across the ovary in June and notice that there are six ovules in it. In the ripe fruit observe that the cup separates easily from the nut. Remove the shell (pericarp) of the nut. How many seeds does it contain? What do you think has become of the other five ovules? Cut through the seed and observe the two cotyledons. Compare the fruits of the beech. Notice that they are three-sided nuts (each being a seed enclosed in a woody pericarp); and that two nuts occur together, surrounded by a bristly woody cup which splits, when the nuts are ripe, into four valves. 3. Stone fruits.—Examine a ripe plum. Cut it open and crack the stone to see the single seed. Notice that the pericarp consists of three layers as in the hazel nut, but that here the middle layer is soft and fleshy, and the outer layer is the “skin.” The stone is the inner layer of the pericarp. Is there any special means of liberating the seed? Compare the cherry, and examine the seed and the three layers of the pericarp. Examine the fruits of the blackberry and raspberry, and observe that each consists of several small stone-fruits arranged on the receptacle. 4. Berries.—The gooseberry.—Notice the stalk at the bottom of the fruit, and, at the top, the withered remains of the calyx. Cut across a half-ripe gooseberry and observe the thick, fleshy pericarp enclosing the seeds. Treat a ripe gooseberry in the same way, and [Pg 176] observe that the pericarp has now for the most part become a soft pulp, in which the seeds are embedded. The rest of the pericarp is a membranous skin. Is there any special means of liberating the seeds? Compare grapes, currants, oranges, and vegetable marrow fruits, and notice that the structure of these resembles that of the gooseberry. 5. The apple.—Cut across the receptacle of the flower (apple blossom) and notice how the five carpels are buried in it (p. 106). Trace the formation of the fruit, and see how the receptacle becomes larger and larger during ripening. At the top of the ripe fruit observe the withered remains of the calyx. Cut the apple through across the middle to see the core. This consists of the horny walls of the five carpels and the contained seeds (pips). From what part of the flower is the fleshy, eatable part of the apple derived? Compare the pear.