III. 



The Continuity of the Protoplasm in Plants. 



"\T7TTHIN comparatively recent years a profound change has come 

 VV over our conceptions of plant organisation. Previous to the year 

 1883 we find it stated in the Physiological text-books that : The life 

 of a higher plant is the sum of the separate life-activities of its com- 

 ponent cells; or that " To many, the cell is always an independent 

 living being, which sometimes exists for itself alone and sometimes 

 becomes joined with others — millions of its like — in order to form a 

 cell-colony, or, as Hackel has named it for the plant particularly, a 

 cell-republic." (Sachs' Lect. Physiology.) 



To-day we can no longer regard these assertions as strictly true. 



It has been found that the cell-walls which were supposed to 

 mark the limits of the component individuals of a multicellular plant 

 are not intact, but that, on the contrary, they are covered at definite 

 points with numerous perforations through which fine filaments of 

 protoplasm run, connecting together the protoplasmic bodies of 

 adjacent cells. 



Thus the protoplasm of a many-celled plant, as that of a single- 

 celled individual, forms one mass ; and the phenomenon of cell-wall 

 formation points, not to the compound nature of the plant, but to an 

 adaption by means of which the protoplasm may attain a large 

 extension without losing its coherency, and through which it obtains, 

 moreover, both a support and a protection from external dangers. 



When the doctrine of the continuity of the protoplasm throughout 

 the plant body, or at least throughout large areas of it, is realised, 

 many problems which were difficult to explain find a ready elucidation. 

 In this respect we may particularly mention the transmission of 

 stimuli from cell to cell. For instance, if the terminal leaflets of a 

 compound leaf of the well-known sensitive plant be touched, these will 

 close together ; but the response does not end here ; on the contrary, 

 the stimulation will be communicated from leaflet to leaflet until it 

 reaches the base of the whole leaf, which will in consequence become 

 depressed. There is little doubt that it is the living protoplasm which is 

 the active agent in this phenomenon of transmission ; but, on the 

 supposition of the isolated nature of the protoplasmic bodies of the 

 separate cells, it is not clear how the stimulus is conveyed from cell 

 to cell. With the knowledge of the continuity of the protoplasm before 



