THE STEM 



87 



mitted from the part in contact — stimulus, in this sense, 

 denoting the influence of any external agent that calls forth 

 a responsive adjustment on the part of the plant. 



99. The object of the 

 various habits of stem 

 growth. — To bring the 

 growing parts of the plant 

 into the best possible rela- 

 tions with light and air is 

 one of the special func- 

 tions of the stem, and the 

 various habits of growth 

 described in this section 

 have been developed with 

 reference to this function. 

 In the case of prostrate 

 and underground stems 

 other factors may intervene ; 

 can you name some of the 

 causes that might influence 

 the position of the stem in 

 such cases ? 



i'lG. lUU. — tjhowiiig the ecouoniy of 

 labor and building material effected by the 

 climbing habit. Notice how the g^ape^'ine 

 coils like an anaconda around the tree 

 boles, and overtops their tallest branches. 

 Compare the diameter of the vine with that 

 of the trees. 



Practical Questions 



1. Why is the normal direction of most stems upright? (Exp. 56.) 



2. Name a dozen woody-stemmed plants; a dozen with herbaceous 

 stems. 



3. Name all the plants you can think of that have prostrate st^ms, or 

 leaf rosettes that hug the earth, like mullein and dandelion. Which of 

 these are wintergreen plants ? Which are hot-weather growers ? 



4. Can you explain in what ways both hot-weather and cold-weather 

 plants may be advantaged by the habit of clinging close to the earth ? 

 (94, 95.) 



5. Is there any difference in the height of the stem of a dandelion flower 

 and a dandelion ball ? 



6. Of what advantage is this to the plant? (Exp. 17.) 



7. Name all the means you can think of by which a stem may climb, 

 and give an example of each. 



