350 THE BIOLOGY OF THE PLANT 



you account for the results obtained? How 

 mucli does the stem grow in length in one 

 year ? Is the growth even ? How many inter- 

 nodes are there on the specimen examined? 

 Notice the leaf-scars. Where are they found ? 

 How do you distinguish them from other parts 

 of the stem ? What is their position with refer- 

 ence to one another ? Are all at the same dis- 

 tance apart ? What is their shape ? Examine 

 the small points, the ends of the fibro-vascular 

 bundles of the leaf, found in each scar. How 

 many are there? Is the number constant? 

 How are they arranged? What relation do 

 the leaf-scars bear to the buds ? 



Examine the bark on an internode. I^ote 

 its color and thickness. Notice the breaks in 

 it on the lower internodes. Do you find them 

 also on the upper ones? Why? In what di- 

 rection do these breaks run ? How do you ac- 

 count for them ? Examine the small, wart-like 

 points, the lenticels, on the bark. Do they 

 have any regular arrangement? How many 

 are there on an internode ? Carefully peel off 

 the bark to see whether the lenticels originate 

 in the bark itself or in the tissues below. With 

 a sharp knife or scalpel cut crosswise through 

 the middle of the first internode of the stem ; 

 make also a longitudinal section through the 

 middle of the internode, and note that the 

 stem consists of the following layers, named in 

 order from the outside towards the centre. 

 2. The brown bark. — In addition to the features 

 already observed, note its thickness as com- 

 pared with the other layers. Do you find any 



