88 PRACTICAL COURSE IN BOTANY 
8. Why do we support peas with brush, and hops or beans with poles? 
(98; Exp. 54.) 
9. Are the vines of gourds, watermelons, squashes, and pumpkins 
normally climbing or prostrate? How can you tell? (96, 97.) 
10. Why does not the gardener provide them with poles or trellises to 
climb on? 
11. Do twining plants grow equally well on horizontal and upright 
supports? (98; Exp. 54.) 
12. If there is any difference, which do they seem to prefer? 
13. Can you give any reasons for thinking that the climbing habit 
might lead to parasitism? (83, 85, 87.) 
14. What method of climbing would be most favorable to the develop 
ment of such a habit? (Suggestion: What mode of climbing brings the 
stem into closest contact with its support ?) 
15. Name some plants the stems of which are used as food. 
16. Name some from which gums and medicines are obtained. 
17. Explain how it can benefit a plant to have its leaves, or some of 
them, modified into tendrils. (99.) 
18. In what way is the loss of the normal function of the leaves so modi- 
fied, compensated for? (Exp..57.) 
19. Suppose the vine shown in Fig. 100 had to lift itself without the aid 
of a support; could it reach the same height and carry the same weight 
of foliage and flowers with the same expenditure of labor and building 
material ? 
II. MODIFICATIONS OF THE STEM 
Materiau. — A shoot of asparagus; thorny branches of locust, plum, 
or haw; a cactus plant; bulbs of lily and hyacinth or onion; tubers of 
potato; rootstocks of iris, fern, or violet. If fresh specimens are not acces- 
sible, dried rootstocks of the sweet flag and Florentine iris may be obtained 
at the drug stores under the names of calamus and ‘‘orris’’ root. 
100. How to recognize modified parts. — Stems, like 
roots, are often modified to serve other than their normal 
purpose, and in adapting themselves to these new functions 
they sometimes undergo such changes of form and structure 
that it would be impossible to recognize their true nature 
from appearances alone. The safest tests in such cases 
are: (1) by a comparison of the parts of the modified struc- 
ture with those of known organs of the same kind; and (2) by 
observing its position in reference to other parts. For 
