52 PRACTICAL COURSE IN BOTANY 



4. Which grows more rapidly, a young shoot or an old one ? (31, 50.) 



5. Which, as a general thing, are the more rapid growers, annuals or 

 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. 



