"Those are both right," said the Chief Gardener. "The blackberry has three parts like the bean, and the tomato has a good many parts. There are some leaves that are compounded as many as four times—each little stem being compounded over and over until there are hundreds of little parts, and yet all are connected with the main leaf-stem which joins the stalk or branch, making really only one leaf. Of course, it is not always easy to tell about leaves, any more than about flowers. Sometimes shapes are so peculiar that it is almost impossible to tell just what they are. Pine-needles are leaves, but it is hard to tell whether they are simple or compound, and it would be hard to tell whether the pine was an Exogen or an Endogen if we had only the needles to go by."
"But you haven't told us how to tell that by the leaves at all," said Davy. "That is what we started to find out."
"That's so, Davy. It's hard to keep to the subject in botany. There are so many things, and all so interesting."
The Chief Gardener took up the lily leaf and that of the blackberry, and held them up to the light.
"Do you see the difference?" he asked.
"Why, yes," said Prue, "the blackberry is all criss-crossy, and the lily leaf runs straight and smooth."
"Those are the veins," said Davy; "I heard Mamma say so."
"Yes, they are the veins," nodded the Chief Gardener, "and when they form a network, or run criss-crossy, as Prue says, it means that the plant is an Exogen. When they run side by side smoothly, as they do in corn and grass, it means that the plant is an Endogen. There are a few of both kinds which do not quite follow this rule, like the pine-tree, which is an Exogen, but has its little straight-grained needles, or like smilax, which has netted leaves, but is an Endogen."
II