182 THE CAUSES OF SPECIFIC SHAPE 



connexions 1 . Possibly special results may be produced in this way by the 

 completion of organs or parts of organs absent from certain protoplasts. It 

 is, however, uncertain to what extent this occurs during normal growth, for 

 the mere awakening of reactions in the protoplast of which it is in itself 

 potentially capable affords no proof. 



Further, protoplasmic threads may convey stimulatory or nutrient 

 substance in mass or by diffusion, which could not otherwise pass from cell 

 to cell 2 . It is also possible that the potential differences created by trans- 

 location may cause the propagation of chemical or physical actions and 

 reactions which act as stimuli. In all life we are in the last resort dealing 

 with molecular movements, and hence we can in all cases regard stimuli as 

 being transferred by special tonic or molecular vibrations 3 . 



The movement of a cilium after local excitation shows that a stimulus can be 

 rapidly propagated through a thin thread of hyaloplasm. As regards the rapidity 

 of propagation of chemical action, the explosion of nitro-glycerine travels at the 

 rate of 1,300 metres per second, whereas the rapid change of colour produced when 

 yellow iodide of mercury is touched at one point by the red form can be followed 

 with the eye. Similarly when a crystal is placed in a saturated solution, the process 

 of crystallization travels rapidly through the solution, and since this occurs in the 

 finest capillary tube, the reaction can be propagated to a great distance. 



A reaction connected with a movement of material would be propagated 

 through a thread of protoplasm or of liquid, if at one end a dissociated ion were 

 continually fixed or removed, and this might be aided by the action of an electric 

 current. A slower diffusion-current would be produced by the continued removal 

 at a given point of any substance generally distributed in solution. In both cases 

 a stimulating effect might be exercised in this way on neighbouring cells, and in fact 

 the metabolism is responsible for numerous regulatory influences. 



Probably various modes are adopted for the transference of stimuli even 

 in the same connecting thread. Moreover the properties and conducting 

 power of the threads may vary according to the conditions, and may not be 

 the same in all the threads radiating from a particular cell. Furthermore, 

 the interactions between dissimilar cells and tissues must result in the 

 production of a maze of crossing and fusing messages. It must also be 

 remembered that the result does not depend so much upon the stimulus as 

 upon the properties of the reacting cell or organ, and that even in the 

 individual protoplast the infinite variety of possible combinations of the 

 available means of response may lead to most varied results. We may 

 remind ourselves that different commands may pass through the same 



1 A transference of the nuclei in vegetative cells has been observed by W. Arnoldi, Flora, 1900, 

 p. 194. Cf. also Miehe, Flora, 1901, p. 115; [Farmer, Nature, 1903]. 



2 Pfeffer, Energetik, 1892, p. 272. 



3 Cf. Nageli, Theorie d. Abstammungslehre, 1884, p. 58. 



