EXTERNAL CONDITIONS ON PLANT LIFE. 



the hotter part of the day, you will find these leaflets constantly 

 rotating, maintaining their parallelism to the sun's rays. If the 

 day is cloudy and the heat of the sun obscured, these same 

 movable sensitive leaflets may remain in a stationary position 

 so as to receive the most direct light possible during the whole 

 day. If you choose to wander in your nearest woods, many 

 similarly-acting plants cannot fail to escape your notice, such 



PLATE No. 6. PLATE No. 7. 



as the Desmodium, the Lcspcdeza, the Mclilotns, and, among 

 the tree-like forms, Amorpha, and Robinia, or the Locust. 



Plate No. 4 shows the Mclilotus, or Sweet Clover, on a cool, 

 moist, somewhat cloudy morning, when the leaves are spread 

 out fully, striving to receive all the light and warmth possible. 

 The direction of the light is generally at right angles to the 

 surface of the foliage. 



Plate No. 5 represents another plant on an extremely hot, 

 dry morning in midsummer, photographed at nine o'clock. 



