536 POPULAR SCIENCE MONTHLY. 



reception of contact stimuli, is applicable to our present case, since lie 

 has shown that the organs for intensifying the effect of contact are sim- 

 ilar in the two kingdoms. No one supposes that the whisker of a cat 

 and the sensitive papilla of a plant are phylogenetically connected. 

 It is a case of what Eay Lankester called homoplastic resemblance. 

 Necessity is the mother of invention, but invention is not infinitely 

 varied, and the same need has led to similar apparatus in beings which 

 have little more in common than that both are living organisms. 



But, whether we are or are not affected in our belief by the general 

 argument from analogy, we can not neglect the important fact that 

 Kreidl proves the possibility of gravisensitiveness depending on the pos- 

 session of statoliths. We must add to this a very important considera- 

 tion — namely, that we know from Nemec's work that an alteration in 

 the position of the statoliths does stimulate the statocyte. Such, at 

 least, is, to my mind, the only conclusion to be drawn from the remark- 

 able accumulation of protoplasm which occurs, for instance, on the 

 basal wall of a normally vertical cell when that wall is cleared of sta- 

 toliths by temporary horizontality. The fact that a visible disturbance 

 in the plasmic contents of the statocyte follows the disturbance of the 

 starch-grains seems to me a valuable contribution to the evidence. 



There is one other set of facts of sufficiently general interest to find 

 a place in this section. I mean Haberlandt's result, also independ- 

 ently arrived at by myself, that when a plant is placed horizontally 

 and rapidly shaken up and down in a vertical plane the gravistimulus 

 is increased. This is readily comprehensible on the statolith theory, 

 since we can imagine the starch-grains would give a greater stimulus 

 if made to vibrate on one of the lateral walls, or if forced into the pro- 

 toplasm, as Haberlandt supposes. I do not see that the difference in 

 the pressure of the cell-sap on the upper and lower walls (i. e., the 

 lateral walls morphologically considered) would be increased. It 

 would, I imagine, be rendered uneven ; but the average difference would 

 remain the same. But in the case of the starch-grains an obvious new 

 feature is introduced by exchanging a stationary condition for one of 

 movement. And though I speak with hesitation on such a point, I am 

 inclined to see in Haberlandt's and my own experiments a means of dis- 

 tinguishing between the pressure and statolith theories. Noll, how- 

 ever, considers that the shaking method is not essentially different from 

 that of Knight's experiment, and adds that the result might have been 

 foreseen. 



