352 THE BIOLOGY OF THE PLAIfT 



extend f hrough the entire stem ? In what part 

 of the stem is the pith relatively greatest in 

 amount ? Of what use is it ? 

 Make drawings of cross and longitudinal sections of 

 the internode, showing the disposition of the tissues. 

 T. The node. — How is it formed? How do you 

 distinguish it from the internode? How does 

 it compare in length with the internode? Is 

 the arrangement of tissues in the node the 

 same as in the internode ? What relation does 

 the node bear to the leaf-scars ? To the buds ? 

 To the side branches ? 

 Examine and compare with the horse-chestnut stem 

 stems taken from the elm, maple, willow, cherry, and 

 pine, and make drawings showing the structures ob- 

 served. Study the stems of herbaceous plants like the 

 Begonia, Tradescantia, strawberry, etc. Make draw- 

 ings of these stems. 



Microscopic Structure. 



Make cross-sections of the last internode of a 

 branch of the horse-chestnut taken in the winter, 

 mount some of the best in water or dilute glyce- 

 rine, and study under the low power. Note the 

 general arrangement of the tissues seen in the 

 cross-section in the study of the gross anatomy 

 of the stem — the brown bark or cork, enclos- 

 ing a chlorophyll - bearing layer, the cortical 

 parenchyma, within which comes a ring of 

 thick - walled fibres of sclerenchyma, the bast 

 fibres, this being intimately associated with the 

 soft bast which shades into a ring of small cells, 

 the cambium, with granular contents. Then 

 comes the wood or xylem, some of Avhose ele- 



