110 PROCEEDINGS OF THE ACADEMY OF [1899. 



uucliscovered these miuute organism? may play an important part 

 in the origin of form. In this case nothing but the advance toward 

 fructification wouhl have furnished ground for suspicion that the 

 leaf was not in a normal condition. 



XII. The MOVEMENTS OF PLANTS. 



What is known as Heliotropism has never been clearly under- 

 stood. Much that has been referred to the action of the sun may 

 be attributable to other causes. When Moore sang: 



"As the sunflower turns on her God, when he sets, 

 The same look which she turned when he rose," 



he expressed the prevailing thought that the plant, in an active 

 sense, sought the sun or avoided the sun, as the case might be, 

 and not that the sun was the acting direct agent in drawing the 

 flower unwillingly along. 



On August 20, 1898, I was passing a large mass of Heliantlius 

 orgyalls at about sundown, and noted that they were taking a wide 

 curve toward the northeast, the stronger plants making a curve of 

 nearly a foot in diameter. As the thermometer had been ranging 

 between 80° and 90° Fahr., I passed on with a general impression 

 that excessive transpiration had induced wilting. On the evening 

 of the 25th, observing again this general northeast curve, I 

 attempted to lift one of the curved points, and was surprised to 

 find the stem at that point rigid, and not flaccid, as it would have 

 been if suffering from lack of moisture. Careful and continued 

 observation was decided on. 



On the 26th, at 6.30 P.M., the stalks Avhich at sundown the 

 previous evening were curving northeast Avere now erect. On the 

 27th, at 6 P.M., the stalks were curving again northeastwardly. 

 On the 28th, at 11.30 A.M., all were curving slightly southwest, 

 and by 2 P.M. the same day were nearly erect. At 6 P.M., 

 with their usual curve northeast. 



On the 31st, at 6.30 A.M., found the first deviation from that 

 general plan in having the curves northeastwardly, instead of 

 having erect stems. At noon they were erect, except a few of the 

 weaker ones which had a northwestern curve. It should be here 

 noted that the terminal flower, which in this and many other com- 

 posite plants is the first to open, while the side branches rapidly 

 <levelop, was now expanding, but many of the stronger branchlets 



