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 | ae = 
other factors may intervene; Fic. 100.—Showing the economy of 
ean you name some of the sborand nulaing material efertd bythe 
causes that might influence coils like an anaconda around the tree 
ih ‘if f th t . boles, and overtops their tallest branches. 
€ position 0 € stem 1n Compare the diameter of the vine with that 
such cases? 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 stems, 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 het-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, 
