THERE ARE JUST TWO KINDS OF LEAVES
A GOOD many things were ripe in August, and some of the things were through blooming. Prue did not plant a great deal. It was too hot to dig long in the sun, and then there did not seem to be much in the way of flowers that could be planted so late. Davy planted a few turnips and some late beans and salad, because there was time for these, but even Davy found it pleasanter to sit in the shade, where there was a breeze, and pull plants to pieces and talk about Exogens and Endogens and the different parts of things, than to hoe and dig and rake on an August day.
The Chief Gardener heard quite loud voices under the peach-trees, one warm afternoon. Prue and Davy were not really quarreling, but they seemed to be a good deal in earnest about something. The Chief Gardener went over there.
"What is all the excitement?" he asked.
Davy held up and waved a large stem of very coarse grass.
"It's an Endogen," he said, very decidedly, "isn't it, Papa?"
"It isn't at all, is it, Papa?" eagerly asked little Prue.
The Chief Gardener took the plumey stem and sat down.
"Why do you think it is an Endogen, Davy?" he asked.
"Because it's a grass, and belongs to the grass family. And corn belongs to the grass family, too, and corn is an Endogen, for it has a big pith instead of rings. So if corn is an Endogen, grass is, too."
The Chief Gardener smiled.
"Well, that's pretty good, Davy, and is true enough, but it isn't just the best way to reason. Now, Prue, why did you think it was an Exogen?"
"Because the stem is hollow, and makes a ring when you cut off a little slice of it, and because the bloom part is in five pieces."
"Sharp eyes," nodded the Chief Gardener, "but Davy is right. There is not always a pith in the endogens. Pipe-stems and fish-poles are hollow, but the cane we make them of is an Endogen, too. And as for the bloom part of this grass, it is a sort of a tassel, like that of the corn. The real blooms are very tiny—too small for us to examine. And then, perhaps, some insect or bird has nipped some of it away. I think I must tell you a little more about leaves, so Davy won't have to know that grass is an Endogen because corn is, and so you won't be mistaken. Suppose, Davy, you try to tell me how many kinds of leaves there are."
Davy looked quite helpless.
"It would take a hundred years," he said.
"Why, no," said Prue. "There are just two kinds. Exogens and Endogens."
Davy laughed, and the Chief Gardener laughed with him.
SOME SIMPLE LEAVES
"But you are right, Prue, in one way," he said. "There are just two kinds of leaves—simple and compound. A simple leaf is a leaf of just one blade, like a grass leaf, or the leaf of a morning-glory. A compound leaf is a leaf made up of several blades, like a bean leaf, which you know is divided into three parts. Of course, there are hundreds of shapes and thousands of species of leaves, but there are just two great kinds, simple and compound. Suppose, Davy, you look about and bring me three compound leaves, and you, Prue, try to find three simple leaves, and let's see what they are."
The children jumped up quickly, and wandered out into the sunny garden, looking as they went. The Chief Gardener heard them chatting, as they looked this way and that. Presently they returned with what they had found. Little Prue climbed up in his lap.
PINE-NEEDLES ARE LEAVES
"Look at mine first!" she said, holding them out, and fanning herself with her little hat.
Davy sat down by them, and looked his collection over to be sure they were right.
"Well, Prue, let's see what you have," began the Chief Gardener. "One peach leaf—that's simple enough. Then here's a lily leaf—that's simple, too. But what's this? It looks as if it came from a Virginia creeper. But where's the rest of it? That's only part of a leaf."
"I told Prue that," said Davy, "and I brought a whole one for one of my compound leaves."
Davy held up what he had brought. The Chief Gardener took the stem of the Virginia creeper. Branching from it were five little stems with a small leaf on each. Prue had taken one of these to be a complete leaf, when it was really only a part of one compound leaf divided into five parts.
"You see, Prue, there is only one stem that joins the main stalk," explained the Chief Gardener. "Whatever branches out from that stem is a part of that leaf. What else have you brought, Davy?"
Davy held up a blackberry leaf, and the leaf of a tomato.
"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