ii8 



BIOLOGY AND HUMAN LIFE 



Fig. 69. Adventitious roots 



If the leaf (or even a piece of leaf) of a bryophyl- 

 lum be placed on damp earth or sand, tiny roots 

 will form at certain points along the edge. Buds 

 will also be produced, so that after a while we can 

 separate small but complete plants and get these 

 to grow into full-sized individuals. The same 

 results can be obtained with the common house 

 plant begonia 



Fig. 70. Climbing roots 



The English ivy, like many other climbing plants, 

 clings to its support by means of adventitious 

 roots that grow out all along the stem. The poison 

 ivy also climbs by means of adventitious roots, 

 and in some of the tropical tree-climbing plants 

 the roots are fully developed as holdfast organs 



stem is then cut away. 

 A similar process takes 

 place naturally in the 

 strawberry plant: its 

 creeping stems bear a 

 cluster of new roots at 

 each tuft of leaves, so 

 that in the course of 

 a season a single plant 

 may spread out and 

 cover a large area. 



Roots that originate 

 from stems or leaves 

 are called adventitious 

 roots (see Fig. 70). 

 In the Indian corn and 

 some other plants ad- 

 ventitious roots serve 

 as props (see Fig. 71). 

 The banyan tree of 

 Asia puts forth sup- 

 porting adventitious 

 roots from the hori- 

 zontal branches. 



96. The stem. Con- 

 necting the leaf with 

 the root is the stem, 

 which is both an organ 

 of support and an or- 

 gan of transportation. 

 The water and salts 

 from the roots pass 

 through one set of 

 tubes, and the manu- 

 factured food from the 

 leaves through another. 



