4 o THE POPULAR SCIENCE MONTHLY. 



and an added significance is given to the following words of Dar- 

 win, with which he closes his memorable work : " We believe that 

 there is no structure in plants more wonderful, as far as its func- 

 tions are concerned, than the tip of the radicle. If the tip be 

 lightly pressed, or burnt or cut, it transmits an influence to the 

 upper adjoining part, causing it to bend away from the affected 

 side ; and, what is more surprising, the tip can distinguish between 

 a slightly harder and softer object, by which it is simultaneously 

 pressed on opposite sides. If, however, the radicle is pressed by a 

 similar object a little above the tip, the pressed part does not 

 transmit any influence to the more distant parts, but bends ab- 

 ruptly toward the object. If the tip perceives the air to be moister 

 on one side than on the other, it likewise transmits an influence 

 to the upper adjoining part, which bends toward the source of 

 moisture. When the tip is excited by light, . . . the adjoining 

 part bends from the light ; but when excited by gravitation, the 

 same part bends toward the center of gravity. In almost every 

 case we can clearly perceive the final purpose or advantage of the 

 several movements. Two, or perhaps more, of the exciting causes 

 often act simultaneously on the tip, and the one conquers the 

 other, no doubt in accordance with its importance for the life of 

 the plant. The course pursued by the radicle in penetrating the 

 ground must be determined by the tip ; hence it has acquired such 

 diverse kinds of sensitiveness. It is hardly an exaggeration to 

 say that the tip of the radicle thus endowed, and having the power 

 of directing the movements of the adjoining parts, acts like the 

 brain of one of the lower animals ; the brain being seated within 

 the anterior end of the body, receiving impressions from the sense- 

 organs, and directing the several movements." 



MY CLASS IN GEOMETRY. 



By GEORGE ILES. 



A VIVID recollection of my boyhood is the general disfavor 

 with which my school-fellows used to open Euclid. It was 

 in vain the teacher said that geometry underlies not only archi- 

 tecture and engineering, but navigation and astronomy. As we 

 never had any illustration of this alleged underlying to make the 

 fact stick in our minds, but were strictly kept to theorem and 

 problem, Euclid remained for most of us the driest and dreariest 

 lesson of the day. This was not the case with me, for geometry 

 happened to be my favorite study, and the easy triumph of leading 

 the class in it was mine. As years of active life succeeded my 

 school-days I could not help observing a good many examples of the 



