Some fruits appear to have "favourites"; they seem to prefer that large animals should eat them. If you look carefully at a piece of orange peel, and cut a small piece across, you will see distinctly small resin pits full of a curious essence which gives the characteristic taste to marmalade. This bitter stuff will prevent wasps from touching the sugar. It is, however, a valuable material, and some kinds of lemons, etc., are grown chiefly for this oil, which is obtained by scraping the peel with a little saucer which is studded with short pins. A still more extraordinary fruit is the prickly pear; this is very delicious though very difficult to eat. Indeed, only monkeys and man seem able to enjoy it. The sugary part and the seeds form a little round mass in the inside. The outside part, though also fleshy, contains hundreds of minute mineral needles, which stick in the tongue and lips and cause most painful inflammation. The monkey eats the prickly pear with very great caution, getting his fingers into the top and scooping out the sugary part. Man requires a teaspoon to do this satisfactorily. Another very curious point about these fleshy fruits (and also ordinary ones) is the strength of the seed inside. It does not look very strong. But an orange seed, for instance, will not be in the least injured if you put it between two glass plates and gradually press upon the upper one up to even a pressure of some thirty pounds. Even hemp seed, which seems quite weak, will endure a weight of four pounds. It is impossible to break a prune stone, or to injure a date stone, by standing with your whole weight upon it. Such strength is necessary because many of these seeds are eaten by birds and ground up in their crops with bits of china, stones, shells, and the like, which the birds pick up just to help them in crushing their food. Fruits and seeds would seem to be exposed to some danger when they are lying on the ground. Horses or other heavy animals might tread on them. But the strength of seeds and their shape is such that no harm is likely to accrue. For instance, I arranged a thin layer of garden earth (a quarter of an inch thick) on a glass plate; upon the earth I placed four hemp seeds; then I put a 58-lb. weight on the top of the seeds. They were not in the least injured, although the seed of the hemp is not a particularly tough one. Under such conditions the seed simply slips into the earth. This is made easy for it on account of its shape, which is generally rounded above and below. A transverse section of a seed would be in shape like the arch of a bridge and its shadow in the water, at least in many cases. There are also usually wonderfully thickened cells in the shell or coat of a seed, which makes it tough and strong.