THE STRUCTURE AND FUNCTION OF HIGHER PLANTS 83 



"supernatural" plants * 



KARL C. HAMNER 



First of all, let us supply the foundation by determining just exactly 

 what a plant hormone is — the importance of which cannot be over- 

 emphasized. The name hormone was first applied to substances produced 

 in certain organs of the animal's body and carried by the blood current to 

 other organs where their effects were manifested. Plants, of course, do not 

 have a blood stream, but it has been shown that there are substances pro- 

 duced in certain localities in the plant and transported to other localities 

 where the effects become evident. These have been called plant hormones. 



We are all familiar with the fact that plants turn toward the light. 

 One of our favorite songs contains the following lines, "As the sun- 

 flower turns toward her god when he sets, the same look which she turned 

 as he rose." This is a recognition of the responses of one plant to light. If 

 you have ever grown seedling plants in your room, you may have noticed 

 their tendency to grow toward the window. These responses to hght are 

 brought by a plant hormone. 



Many years ago, early plant scientists were interested in finding out 

 why plants grew toward the light. Working with tiny oat seedlings, grow- 

 ing in dark basements, they found that the plants did not bend toward 

 the light if the tip of the plant was removed. If they removed the tip of 

 the plant and illuminated one side of the tip leaving the rest of the plant 

 in complete darkness, they could cause the plant to bend by putting the 

 tip back on. The plant always bent toward the direction from which 

 the tip had been illuminated. They were able to extract from the tips a 

 substance which would cause the plants to bend even though the tip was 

 not present. They identified this substance as a particular chemical com- 

 pound which they called auxin. Its action on the plant is caused by the 

 fact that it promotes growth in the cells on the side of the plant to which 

 it is applied. When a plant is illuminated on one side this hormone travels 

 down the shaded side of the plant causing greater growth there and thus 

 causing the plant to bend toward the light. 



Undoubtedly, the discovery of auxin has considerable practical value 

 and may make quite a difference in our every day living. The chemist 

 not only has identified naturally occurring auxins, but he has also syn- 

 thesized new compounds which work just as well, or even better, than 

 the ones produced by the plants themselves. These chemical compounds 

 have proven very useful. A solution containing some of these chemicals, 

 or a lanolin paste of them, may be applied to cuttings in order to stimulate 

 a more rapid root formation. Sometimes the rapidity with which roots 



* Reprinted from one of a series of radio broadcasts entitled Excursions in Science, 

 General Electric Company, 1946. 



