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by a prisoner. Although the individual prisoners may be strong men, and 

 be in a frenzied state of activity, beating the sides of rooms, yet a specta- 

 tor looking at the outside of the prison would see no movement of the 

 walls, no evidence of life. With the discovery of continuity of protoplasm 

 between plant cells, an English discovery of 1882, we have learned that to 

 have our illustration really accurate, we should suppose all the cells of the 

 prison to be connected by telephone. We must furthermore provide 

 towers, with walls that are thinner and of flexible material. Now, if an 

 alarm is given, all the prisoners being apprised at once, or nearly so, act 

 in concert. The spectator on the outside sees no movement in the thick- 

 walled part of the structure, but he sees the towers sway. We must 

 further suppose that the men in the thick-walled cells, finding their efibrts 

 are useless, no longer make any response when the alarm is given, while 

 those in the thin-walled cells, finding their efforts rewarded, become con- 

 stantly more active and learn how to combine their efforts for greater 

 efficiency. 



The application to the plant is obvious. Although the force which a 

 plant can exert amounts to several atmospheres, it is only in the young 

 tender portions, usually at the ends of the branches of the stem and root, 

 that this force can be successfully applied to secure movement of the whole 

 organ. It therefore comes about that movement in plants is oftenest as- 

 sociated with growth. This arrangement permits each root tip and grow- 

 ing stem to have its own kind and degree of sensitiveness. Thus we find 

 by experiment that while the first root which starts from a seed, the tap 

 root, is sensitive to gravity in such a way that it places itself parallel to 

 to the direction of the impinging force and points directly downward, the 

 secondary roots, which branch from it, are sensitive after a different fashion, 

 and instead of growing parallel to the force, grow at an angle to it, the 

 exact angle being different for different kinds of plants. The tertiary roots, 

 or next set of branches, are usually very little sensitive to gravity, or if 

 they are sensitive they assume a nearly horizontal position. The stems 

 react in a similar way, except that the general direction is upward instead 

 of downward, and in consequence of the diversity of sensitiveness of the 

 primary and secondary shoots, the branches are spread out to the air and 

 light, imparting to each species of the tree and herb its characteristic ap- 

 pearance. 



But if there is no nerve-like communication between one root tip and 

 another, or between one stem end and another, there is sometimes a dis- 



