104 PHYSIOLOGICAL PROCESSES IN PLANTS 



g. (Optional.) A Study of the Ways Leaves and Stems, 

 etc., protect themselves or Ways in which Plants 

 adapt themselves so as to make a Greater Success of Life 



1. Begonia Leaf. Note the thickness of its epidermis. In what way 

 is this a protection ? 



2. Cactus. What are the leaves of the cactus ? In what way do they 

 protect the plant ? What part does the work of leaves ? 



How does the absence of foliage leaves protect the cactus in its native 

 surroundings ? 



3. Cabbage Leaf. Note the waxy surface. How is this a protection ? 



4. Do leaves fall from trees in hot, dry weather ? How is this of 

 advantage ? Do twigs drop from trees in the autumn ? If so, is this any 

 advantage ? 



5. Of what advantage is it that corn leaves and those of other plants 

 curl on a hot day ? 



6. Examine a section of an India rubber leaf and note the position of 

 the stomata. Is their position of any advantage ? Explain. 



7. Note the position of oxalis, or white clover, or squash seedlings, by 

 day or by night. What difference of position ? How are these positions 

 a protection to the plant ? 



8. Examine leaves and stem of mullein. What do you find ? Could 

 these hairs protect against insect bites ? Against extremes of temperature ? 



9. How do the following plants protect themselves partially from the 

 attacks of animals (including man) knotgrass, cut-grass, tomato, 

 onion, ragweed, wormwood, bulb of Jack in pulpit, red peppers, mustard, 

 horse-radish ? 



10. Examine the following plants and tell how they protect them- 

 selves, thorn apple, barberry, locust, rosebush. 



11. How may spines be especially helpful in regions to which cacti 

 are peculiar ? 



12. Fill in the following summary : 



ENEMIES OF PLANTS 



How PLANTS PROTECT THEMSELVES FROM THEIR ENEMIES 



