LESSONS WITH PLANTS 



305 



to the light. Annual plants have soft or herbaceous stems. 

 Perennial shrubs, vines, and trees have hard and woody 

 stems. Compare them. Cut across a young, herbaceous 

 stem hke a cornstalk and note the thread-Uke strands that 

 run through it. These may be 

 shown better by cutting through 

 the hard outer layer of the stalk 

 and breaking and puUing apart 

 the rest, when the strands will ap- 

 pear as threads projecting out 

 from the stalk. These strands 

 are found in all stems and are 

 very important. They consist 

 partly of strong cells that give 

 rigidity and strength to the stem, 

 and partly of duct -hke or tubular 

 cells that allow the sap to flow 

 through them. These strands of 

 strengthening and conducting tis- 

 sues are called, technically, fibro- 

 vascular bundles, and serve as a 

 sort of skeleton for the plant and as its circulatory system. 

 Some ducts convey sap up, while others let it down to the 

 root. 



In plants that have two cotyledons or seed leaves in the 

 seed, as for example, the pea, bean, sunflower, geranium, 

 squash, box-elder, lilac, etc., the fibrovascular strands are 

 arranged in a ring around a central pith. Cut across a 

 young sunflower stem or young lilac shoot and this can be 

 seen. Press the stem and see the water exude from cer- 

 tain parts of the ring. Here are the tubular conducting 



Fig. 1 10 Fibrovascular Strands in 

 Plantain Leaf. 



