rEBBUAK¥ 2, 1917] 



SCIENCE 



103 



meable to the red pigment, which begins to 

 diffuse out into the surrounding protoplasm. 

 This change begins soon after the cell is 

 touched. As the red pigment diffuses 

 through the protoplasm it soon reaches 

 neighboring chromatophores and it may be 

 seen that their surfaces also become per- 

 meable and their pigments begin to diffuse 

 out. In this way a wave — which may be 

 compared to a wave of stimulation — pro- 

 gresses along the cell until the opposite end 

 is reached. 



The rate of propagation of this wave cor- 

 responds to that of the diffusion of the pig- 

 ment. It would seem that at the point 

 where the cell is touched, pigment, and 

 probably other substances, are set free, dif- 

 fuse out and set up secondary changes as 

 they progress. These changes are doubt- 

 less chemical in nature. 



The important question then arises : How 

 does the contact initiate the outward dif- 

 fusion of the pigment or other substances? 

 It would seem that this may be due to a 

 mechanical rupture of the surface layer of 

 the chromatophores which is either not re- 

 paired at all or only very slowly. Many 

 cases are known in which the surface layers 

 of protoplasmic structures behave in this 

 way. If, therefore, such structures exist 

 within the cell, it is evident that any de- 

 formation of the protoplasm which is suffi- 

 cient to rupture their surface layers will 

 permit their contents to diffuse out into 

 the surrounding protoplasm. A great vari- 

 ety of cellular structures (plastids, vacu- 

 oles, "microsomes," inclusions, etc.), pos- 

 sess surface layers of great delicacy and it 

 is easy to see how some of these may be 

 ruptured by even the slightest mechanical 

 disturbance. 



If these processes occur it is evident that 

 purely physical alterations in the proto- 

 plasm can give rise to chemical changes. 

 Responses to contact and mechanical stim- 



uli may be thus explained ; and since gravi- 

 tational stimuli involve deformation of the 

 protoplasm we may extend this conception 

 to geotropism. 



Further studies, which are now being 

 made, can not be mentioned for lack of 

 time, but it is hoped that what has been 

 said may suffice to indicate how stimula- 

 tion, vitality, injury and recovery, together 

 with permeability and antagonism, may 

 be brought under a common point of view 

 and pei'haps traced to similar fundamental 

 causes. W. J. V. Osterhout 



Laboratory op Plant Physiology, 

 Harvard University 



JOHN MUIRi 



It is as a human being ever striving up- 

 ward that I would portray John Muir. 



From his early boyhood to his old age this 

 spirit dominated him. As a child in Scot- 

 land, at every opportunity, in spite of parental 

 prohibitions, and notwithstanding the cer- 

 tainty of punishment upon his return, he 

 would steal away to the green fields and the 

 seashore, eagerly interested in everything alive. 



Illustrating this trait, I quote his boyhood 

 impressions of the skylarks :^ 



Oftentimes on a broad meadow near Dunbar we 

 stood for hours enjoying their marvelous singing 

 and soaring. From the grass where the nest was 

 hidden the male would suddenly rise, as straight 

 as if shot up, to a height of perhaps thirty or 

 forty feet, and, sustaining himself with rapid 

 wing-beats, pour down the most delicious melody, 

 sweet and clear and strong, overflowing all bounds, 

 then suddenly he would soar higher again and 

 again, ever higher and higher, soaring and singing 

 until lost to sight even in perfectly clear days, and 

 oftentimes in cloudy weather "far in the downy 

 cloud" . . . and still the music came pouring 

 down to us in glorious profusion, from a height 

 far above our vision, requiring marvelous power of 



1 Address delivered upon the occasion of the un- 

 veiling of a bronze bust by the sculptor C. S. 

 Pietro, at the University of Wisconsin, December 

 6, 1916. 



2 ' ' The Story of My Boyhood and Youth, ' ' John 

 Muir (Houghton-MiflBin Co., 1913), pp. 46 and 47. 



