STEMS 111 



presents a new coat of smooth, clean, greenish 

 white bark to the weather. The bark serves to 

 protect the layer of living tissue from damage by 

 the climate, or by animals, or from the falling 

 trunks or branches of other trees. On the other 

 hand, the numerous crevices afford lodgment and 

 refuge for the spores of parasitic fungi which ger- 

 minate and injure the tree, and also harbors insects 

 and other animals which work injury in many 

 ways. 



151. Growth of a corn stem. — Select a young 

 and rapidly growing corn stem and mark off three 

 or four of the terminal internodes into half-inch 

 intervals by means of India-ink. Measure these 

 from day to day for a week. What places show 

 elongation ? 



Trees are generally larger at the bases, but in the 

 corn plant and in the palms and their relatives the 

 basal part of the stem will be found to be smaller 

 than parts of the stem above it. This is due to 

 the fact that such stems soon reach their full growth 

 in thickness at the base, and the later portions 

 formed may receive more food and attain a greater 

 thickness. 



