英文科學(xué)讀本 第三冊·Lesson 56 The Single Seed-Leaf

Lesson 56 The Single Seed-Leaf

Fred, you promised to tell me about those plants whose seeds have a single seed-leaf, said Norah. "Did you get your lesson today?"

Yes, said Fred, "we had our lesson, and I'll try and tell you all I can about it, if you would like to hear it."

To make us understand these seeds properly, teacher brought some grains of Indian corn for us to examine. Some of the grains he had kept in soak for a few days, so that instead of being hard and brittle, they were soft enough for him to cut easily. He gave me some of the soaked grains after the lesson. Here they are. I'll try and show you what teacher showed us in class. Don't laugh if I can't do it so well as he did, Will. Here, lend me your knife. It's sharper than mine.

Well, he continued, "teacher took one of the grains and cut away with his knife, like this, all the outside mass of soft substance, and presently—bravo! I've done it."

Done what, Fred? asked Norah.

Why, look; all this outside stuff has nothing to do with the actual seed. Here is the seed. It was embedded in the middle of the grain.

Now suppose we have a look at the seed itself. See, Norah, it has a plumule and a radicle, just like other seeds. But I want you to notice the outer part of the seed. This, you see, is all in one piece, and folds itself completely round the plumule and radicle as if to protect them. You remember, of course, that the germs of the other seeds are protected by double seed-leaves. This has only a single seed-leaf.

Now think of our old lessons on the grain plants, and you will be able to tell me what kind of leaves they all have, corn as well as the rest.

These all have parallel-veined leaves, said Norah. "The veins run through the leaves, side by side, from base to tip."

Remember, then, said Fred, "that all plants bear parallel-veined leaves that come from seeds with a single seed-leaf."

Does the little seedling get its food from this one seed-leaf, Fred?

No, Norah, said Fred. "In all these seeds the food store is laid up in the grain, which surrounds the germ, and not in the seed-leaf. The seed-leaf itself is not thick and solid like those of the bean."

SUMMARY

The germ of the grains has only one seed-leaf. The food-store to feed the growing germ is laid up in the grain itself, and not in the seed-leaf. All plants that grow from such seeds have parallel-veined leaves.