INTRODUCTORY SURVEY 21 



30. Which of these four divisions contains the most plants useful for 

 food? 



31. In which of these four divisions are the largest plants found? 

 In which the smallest? 



32. To which of these four divisions do plants growing in the ocean 

 chiefly belong? To which do land plants chiefly belong? 



33. Name some Thallophytes which are useful to man and some which 

 are harmful. Name some Spermatophytes which are useful and some 

 which are harmful. 



34. Which of the four divisions contains the largest number of plant 

 species which are harmful to man and to his domestic animals and 

 plants? Which contains the largest number of useful species? 



35. Bryophytes and Pteridophytes have much fewer species than 

 either Thallophytes or Spermatophytes. What reason can you suggest 

 for this fact? 



36. Under what climatic conditions are Pteridophytes most conspicu- 

 ous and abundant? 



37. What are the advantages of organization (the "division of labor") 

 in a plant? 



38. Which of the four main divisions of plants do you think shows 

 the highest degree of organization within its plant body? 



39. In general, do you think that it has been the most highly organized 

 or the less highly organized plants which have been most successful? 

 Explain your answer. 



40. Why are living things called "organisms?" 



41. Are the most important agricultural crops derived from the 

 root, the stem, the leaf, or the fruit? Explain. 



42. Roots are confined almost entirely to land plants. Explain. 



43. Give an example of a root which serves as a store-house for a 

 large amount of food. 



44. What advantage has the root over the stem as a place for food 

 storage? 



45. Name ten cultivated plants in which the root is the organ useful 

 to man. 



46. Name a few plants in which the stem is very much reducetl. 

 Under what important disadvantage are such plants? 



