“Sort of a slender diet,” remarked Roger, who was blessed with a hearty appetite.

“The leaves give it a lot of food.  I was reading in a book on botany the other day that the elm tree in Cambridge, Massachusetts, under which Washington reviewed his army during the Revolution was calculated to have about seven million leaves and that they gave it a surface of about five acres.  That’s quite a surface to eat with!”

“Some mouth!” commented Roger.

“If each one of you will pick a leaf you’ll have in your hand an illustration of what I say,” suggested Helen.

[Illustration:  Lily of the Valley Leaf]

They all provided themselves with leaves, picking them from the plants and shrubs and trees around them, except Ethel Blue, who already had a lily of the valley leaf with some flowers pinned to her blouse.

“When a leaf has everything that belongs to it it has a little stalk of its own that is called a petiole; and at the foot of the petiole it has two tiny leaflets called stipules, and it has what we usually speak of as ‘the leaf’ which is really the blade.”

They all noted these parts either on their own leaves or their neighbors’, for some of their specimens came from plants that had transformed their parts.

“What is the blade of your leaf made of?” Helen asked Ethel Brown.

“Green stuff with a sort of framework inside,” answered Ethel, scrutinizing the specimen in her hand.

“What are the characteristics of the framework?”

“It has big bones and little ones,” cried Della.

“Good for Delila!  The big bones are called ribs and the fine ones are called veins.  Now, will you please all hold up your leaves so we can all see each other’s.  What is the difference in the veining between Ethel Brown’s oak leaf and Ethel Blue’s lily of the valley leaf?”

[Illustration:  Ethel Brown’s Oak Leaf]

After an instant’s inspection Ethel Blue said, “The ribs and veins on my leaf all run the same way, and in the oak leaf they run every which way.”

“Right,” approved Helen again.  “The lily of the valley leaf is parallel-veined and the oak leaf is net-veined.  Can each one of you decide what your own leaf is?”

“I have a blade of grass; it’s parallel veined,” Roger determined.  All the others had net veined specimens, but they remembered that iris and flag and corn and bear-grass—­yucca—­all were parallel.

“Yours are nearly all netted because there are more net-veined leaves than the other kind,” Helen told them.  “Now, there are two kinds of parallel veining and two kinds of net veining,” she went on.  “All the parallel veins that you’ve spoken of are like Ethel Blue’s lily of the valley leaf—­the ribs run from the stem to the tip—­but there’s another kind of parallel veining that you see in the pickerel weed that’s growing down there in the brook; in that the veins run parallel from a strong midrib to the edge of the leaf.”