498 THE POPULAR SCIENCE MONTHLY. 



DAKWIN ON THE MOYEMENTS OF PLANTS. 



By ELIZA A. YOUMANS. 



SINCE the time of Linnaeus, men have wondered and speculated 

 about what are known as the spontaneous movements of plants, and 

 in recent years the causes of these movements have been carefully in- 

 vestigated by botanists. The subject in its various bearings now forms 

 a large part of the science of vegetable physiology. The periodical 

 and irritable motions of plants, and those due to light and gravity, 

 have been closely studied in connection with the mechanical laws of 

 growth, and many of these phenomena have been more or less satisfac- 

 torily explained. 



But it has been reserved for Mr. Charles Darwin to go deeper into 

 the facts and philosophy of the subject than any of his contempora- 

 ries. In 1875 he published a book upon " The Movements and Habits 

 of Climbing Plants " ; and he has since extended his inquiries so as to 

 include the movements manifested by the entire vegetable series, ex- 

 cept the lowest flowerless plants, and upon these he is now engaged. 

 He has just published an account of these researches in a volume of 

 six hundred pages, uniform with his other works. 



One of the movements of plants long ago observed was described 

 by the term nutation, which simply means nodding. The motion of 

 a flower in following the api3arent movement of the sun from the east 

 in the morning to the west in the evening is an example of nutation, 

 and this kind of motion has been found to be much more extensive in 

 plants than was formerly supposed. 



When we observe the growing stem of the hop, after the first two 

 or three joints ai-e formed, we see it bend to one side and travel slowly 

 round toward all points of the compass, and continue these revolu- 

 tions day and night. This spontaneous gyi-ating motion of stems and 

 tendrils was first remarked by Palm and Mohl, and Professor Sachs 

 gave it the name of revolving nutation. 



Mr. Darwin has found that this kind of motion is ever present in 

 the growing parts of plants, so that it must be regarded as a univer- 

 sal property of growing vegetation, and he suggests for it the better 

 term circumnutation. He has proved that even the buried stems and 

 rootlets of germinating seeds make this movement so far as the sur- 

 rounding pressure will permit. 



By the most ingenious and delicate contrivances, and his own con- 

 stant cooperation, Mr. Darwin has made it possible for the circumnu- 

 tating organs themselves to indicate approximately the direction and 

 extent of their movements. His arrangements for enabling organs to 

 record their motions varied somewhat ; but we give his own account 

 of the general process : 



