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PLANT BIOLOGY 



the top ever develop ? Where do suckers come from ? 

 Where does the ear grow ? 



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 fibers. Which is more abundant ? Do the 

 fibers have any definite arrangement ? Which strands are 

 largest? Smallest? The firm smooth riud { 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 ad- 

 mirably 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 paren- 

 chyma, the tissue from which when young all 

 the other tissues arise and differentiate (Paren- 

 chyma =' parent + chyma, or tissue). 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. W r hen 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 



Fig. 70. — Dia- 

 gram toshow 

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