STEM STRUCTURE 



81 



ference we obtain many of our wood products from the dicoty- 

 ledonous stems, while the monocotyledonous, having little wood 

 and much pith for storage, provide us with foods such as hay 

 and grain, sugar-cane, and starch. 



Do not think that the monocotyledonous stem is weak because 

 it has so little wood tissue the case is quite the contrary as you 

 may prove for yourself. 

 Select a tall grass stem, 

 such as timothy or rye. 

 Measure its height and its 

 diameter. How many 

 times its thickness is the 

 height? Suppose it were a 

 tree one foot in diameter 

 how tall would it be? Com- 

 pare this with the actual 

 height of trees. Figure 

 this out and you will 



jttHacorvi.C.DO/1 o us Trff . 



FIG. 18. Cross section of typical 

 monocotyledonous stem. 



have more respect for the 



strength of the grass stem, as well as for the " sturdy oak." 



Polycotyledonous Stems. Seeds having several cotyledons 

 (polycotyledonous) have a woody stem with annual rings, but 

 differing in other ways from 'the two preceding types. We shall 

 not take up its structure in detail; pines, spruces and all ever- 

 green trees belong to this last group and their resinous wood 

 furnishes us with our best lumber. 



Not only are their stems of great strength, but some of them 

 are the largest and oldest living things in the world. The Big 

 Trees (Sequoia) of California are the oldest, even among trees. 

 One of these ancient giants, the " General Sherman Tree," is nearly 

 four thousand years old, 279 feet high, and 36 feet in diameter. 



To put it another way, it was a flourishing sapling, twenty or 

 thirty feet high when the Exodus of Israel and the Trojan wars 

 took place. It was a thousand years old at the time of Solomon 

 and two thousand at the birth of Christ. All our European and 

 American history are but events of yesterday to this patriarch of 



