NATURE OF PLANTS 69 



that the seeds are unable to grow unless they come in contact 

 with the hypha e of the fungus. Finally some plants have become 

 so adapted to these fungi as to receive all necessary foods from 

 them. Accordingly, their green leaves and roots have largely 

 disappeared since they are no longer of service. Examples of 

 this are seen in the white Indian pipe and pine-sap and in the 

 coral root orchid. In these latter examples the relationship of 

 the two plants is completely turned about for we see that the 

 plant has become a parasite upon the fungus. 



28. Roots as Store-houses for Foods. — In all the cases hereto- 

 fore considered the root has functioned in one way or another as 

 an organ for the temporary reception and transmission of materi- 

 als from the soil. It may also serve in other capacities, one of 

 the more important of which is as a storage organ. Such roots 

 become fleshy and filled with foods and are of great economic 

 importance, furnishing a variety of nutritious vegetables, as the 

 sweet potato, beet, turnip, etc. Many of these valuable plants 

 are bi ennialg . During the first season the plant develops only 

 leaves and stores up food in its fleshy roots which is utilized in 

 the following season in the production of flowers and seeds, after 

 which the plant perishes. It is noteworthy that the biennial 

 habit has been induced in many of these plants by cultivation. If 

 they are left to themselves in a wild condition they will soon 

 revert to an annual growth, i. e., producing seed and perishing 

 during the season. P erenni al plants live on from year to year. 

 As to whether some plants behave as annuals, biennials, or 

 perennials depends in some cases upon the place or time of 

 planting. The castor bean with us is an annual but in warm 

 countries it becomes a perennial. Winter wheat on the other 

 hand has acquired a biennial habit owing to the late planting of 

 summer wheat types. 



29. Anchoring and Supporting Roots. — Roots also play a very 

 important role in anchoring and supporting the plant. Excellent 

 examples of the supporting roots are seen in the Indian corn 

 where numerous roots spring from the stem a short distance from 

 the ground and reach out on all sides like guy ropes steadying 

 the plant in the ground. Similar devices appear in our elms, 



