52 PRACTICAL COURSE IN BOTANY 
4. Which grows more rapidly, a young shoot cr an old one? (31, 50.) 
5. Which, as a general thing, are the more rapid growers, annuals of 
perennials? Herbaceous or woody-stemmed plants? 
6. Name some of the most rapid growers you know. 
7. Of what advantage is this habit to them? 
8. Why do roots form only on the under side of subterraneous stems? 
(51.) 
9. Why do new twigs develop most freely on the upper side of hori- 
zontal branches? (51.) 
Field Work 
(1) Notice the various seedlings met with in your walks and see how 
many you can recognize by their resemblance to the mature plants. Ac- 
count for any differences you may observe between seedlings and older 
plants of the same species. Observe the cotyledons as they come up and 
their manner of getting out of the ground, and notice the ways in which 
this is influenced by moisture, light, and the nature of the. soil. Where 
the cotyledons do not appear, dig into the ground and find out the reason. 
Notice which method of emergence occurs in each case, the arched, or 
straight, and account for it. Observe particularly the behavior of seed- 
lings in hard, sunbaked soil. If you see any of them lifting cakes of earth, 
compare the size and weight of the cake with that of the seed; if there is 
any disparity, what does this imply? What is the force called which the 
plant exercises in lifting the weight? (51.) 
(2) Notice if there are any seeds germinating successfully on top of 
the ground, and find out by what means their roots get into the soil. 
Observe what effect sun and shade, moisture and drought, and the nature 
of the soil have on the process. Find out whether roots exercise force in 
penetrating the soil; what kinds they penetrate most readily, and what 
kinds, if any, they fail to penetrate at all. Notice whether seedlings with 
taproots, like the turnip and castor bean, or those with fibrous roots, like 
corn and wheat, are more successful in working their way downward. 
(3) Look for tree seedlings. Explain why seedlings of fruit trees are so 
much more widely distributed in cultivated districts, and so much easier 
to find than those of forest trees. Where do the latter occur, as a general 
thing? Account for the fact that seedling trees are so much more rare 
than germinating herbs, and why trees like the oak and chestnut and 
black walnut propagate so much more slowly, in a state of nature, than. 
the pine, cedar, ash, and maple. 
(4) Observe the direction of growth in plants on the sides of gullies and 
ravines, and tell how it is influenced by geotropism. Notice whether there 
are other influences at work; for instance, light, or in the case of roots, 
the attraction of moisture. 
