46 LABORATORY STUDIES OF THE STEM 



What is its Position ? 



These are the questions to be kept in mind in the fol- 

 lowing exercise. 



EXERCISE XVII. THE CHARACTERISTIC FEATURES OF STEMS 



Red Maple. Examine with care all marks and features of form 

 and the position of the branches and buds with respect to certain of 

 these markings. Examine especially the newest parts. A low power 

 of the hand lens brings out the desired points well. 



Most trees and shrubs upon the approach of cold weather shield the 

 tender extremities of their stems by numerous scales. When growth 

 is resumed at the beginning of the next season, the scales fall away, 

 leaving scars to mark the occurrence of winter. These are to be looked 

 for on the material in hand, and noted as interesting traces of events 

 in the recent history of the twigs. But such annual demarkations are 

 not to be found on all stems. Refer to the questions immediately pre- 

 ceding this exercise, and answer them in the notes. The sections of 

 the stem at which leaves are borne are called nodes; the lengths 

 between leaves are internodes. 



Draw the terminal, and one or two adjacent, annual lengths of the 

 twig enough to show all the points learned in the study. 



EXERCISE XVIII. THE INTERNAL STRUCTURE OF STEMS 1 



Looking at the plants of the fields about us, we perceive the great- 

 est variety in the size, proportions, and attitude of stems. In some 

 the stem is so short as to seem to be quite wanting, the leaves appear- 

 ing to spring directly from the root. In other cases the stem, elon- 

 gated, reclines upon the ground, or twines for support upon any object 

 within reach. 



Yet there is a prevailing type. Its erect habit and height most 

 clearly show the purpose of stems in general. What is this pur- 

 pose ? 



As height from the ground means encounter with winds, the tall 

 stem must also be strong. Furthermore, the sap has a considerable 

 distance to travel from the root to the leafy crown, and hence 

 the conduction of water becomes one of the functions of the stem. 



1 See also Chapter XVII. If compound microscopes are available, the 

 minute structure may be taken up more in detail than the directions here 

 given require. In any case use should here be made of figures and ex- 

 planations from Chapter XVII. The cambium region, especially, should 

 be located even under the dissecting microscope, and its meaning 

 explained. 



