66 NATURE STUDY MADE EASY 



"What are those lines running across from the pith to the 

 bark?" asked Tom Brown, who had eyes for everything. 



"I don't believe you will remember if I tell you/ 7 said his 

 teacher; "those are called medullary rays. They are formed of 

 lighter wood, and give strength to the stem. Carpenters like 

 them, for they give that grainy look to furniture which makes it 

 so pretty. They are found in woody di cotyledons. " 

 " Have all trees stems like that ? " asked George Hall. 

 "Oh, no; only trees that grow from dicotyledons, like the oak, 

 the maple, the plum/ 7 replied his teacher. 



"Trees that grow from monocotyledons have stems like this; 7 ' 

 and she showed a cross section of a palm tree, while one of the 

 boys drew it on the blackboard. " Here, in- 

 stead of a pith and medullary rays, there are 

 only smooth bark and loose wood. 



"In dicotyledons the bark is soft and 

 broken, and the heartwood, or central wood, 

 CROSS SECTION OF i g strong and firm. That is why these trees 



TRUNK OF PALM TRKE are chogen for building pur p oses . 



"In monocotyledons the bark is hard and strong, while the 

 center is soft and pulpy, because the growth is all outward against 

 the bark, and the wood is pressed closer and closer outward. 



"Dicotyledons grow outward, and are called exogens. 



"Monocotyledons grow inward, and are called endogens. 



"I will tell you a true story to prove this fact/ 7 said the teacher. 

 "Two workmen had been employed for many years in felling timber 



