A piece of _cornstalk_, either green or dead, should be in the hand of each pupil while studying this lesson. Fig. 69 will also be of use. Is there a swelling at the nodes? Which part of the internode comes nearest to being perfectly round? There is a grooved channel running along one side of the internode: how is it placed with reference to the leaf? with reference to the groove in the internode below it? What do you find in each groove at its lower end? (In a dried stalk only traces of this are usually seen.) Does any bud on a cornstalk besides the one at the top ever develop? Where do suckers come from? Where does the ear grow? [Illustration: FIG. 70.—DIAGRAM TO SHOW THE COURSE OF FIBRO-VASCULAR BUNDLES IN MONOCOTYLEDONS.] Cut a cross-section of the stalk between the nodes (Fig. 69). Does it have a distinct bark? The interior consists of soft “pith” and tough woody parts. The wood is found in _strands_ or _fibres_. Which is more abundant? Do the fibres have any definite arrangement? Which strands are largest? Smallest? The firm smooth _rind_ (which cannot properly be called a bark) consists of small wood strands packed closely together. Grass stems are hollow cylinders; and the cornstalk, because of the lightness of its contents, is also practically a cylinder. Stems of this kind are admirably adapted for providing a strong support to leaves and fruit. This is in accordance with the well-known law that a hollow cylinder is much stronger than a solid cylinder of the same weight of material. Cut a thin slice of the inner soft part and hold it up to the light. Can you make out a number of tiny compartments or cells? These cells consist of a tissue called _parenchyma_, the tissue from which when young all the other tissues arise and differentiate. The numerous walls of these cells may serve to brace the outer wall of the cylinder; but their chief function in the young stalk is to give origin to other cells. When alive they are filled with cell sap and protoplasm. Trace the _woody strands_ through the nodes. Do they ascend vertically? Do they curve toward the rind at certain places? Compare their course with the strands shown in Fig. 70. _The woody strands consist chiefly of tough fibrous cells that give rigidity and strength to the plant, and of long tubular interrupted canals that serve to convey sap upward from the root and to convey food downward from the leaves to the stem and the roots._ [Illustration: FIG. 71.—DIAGRAM OF WOOD STRANDS OR FIBRO-VASCULAR BUNDLES IN A ROOT, showing the wood (_x_) and bast (_p_) separated.] Monocotyledons, as shown by fossils, existed before dicotyledons appeared, and it is thought that the latter were developed from ancestors of the former. It will be interesting to trace the relationship in stem structure. It will first be necessary to learn something of the structure of the wood strand.