THE STRUCTURE OF CELLS 



occur throughout the tissues of the organism in those examples which 

 have been specially investigated for the purpose. Thus it is evident 

 that, so far from the syncytial condition presenting an exceptional 

 case, it is in reality an extremely common one, the cell-walls merely 

 forming a perforated skeletal framework which supports the softer 

 parts. It is useless to argue (as has recently been done) that the 

 pores are so fine as to be practically useless for the transference of 

 material substances through them, since, as Horace Brown has shown, 

 their very narrowness, taken together with the thinness of the portion 

 of membrane on which they occur, is an important condition for 

 the performance of such a function without unduly weakening the 

 framework itself. Moreover, the existence of the continuity of the 

 protoplasm from cavity to cavity at once renders intelligible the 



FIG. 2. 



Continuity of protoplasm through vege- 

 table cell-walls. A, cells of the pulvinus 

 of Robinia. B, cells of the endosperm of 

 lleterospathe.. (After Gardiner.) 



possibility of a transmission of stimuli from one part of the body to 

 another, although it would perhaps be going too far to assume this 

 as a necessary condition of transmission. Examples are known in 

 which the stimuli appear to be less directly conveyed, as, for 

 instance, in the case of nerve ganglia, according to Ramon y Cajal 

 (although his results have not been upheld by some other investi- 

 gators) ; and further, in some plant tissues, water squeezed out 

 into the intercellular spaces has been regarded (on rather slender 

 grounds) as being the means of exciting consecutive cells of a tissue. 

 On the other hand, Nemec has recently shown reason for admitting, 

 in the irritable parts of plants, the existence of specialised tracts of 

 protoplasm which are continuous from cell to cell, and by the agency 

 of which the stimulant impulse is conveyed to the motor executive 

 region. Whilst the general and mutual relations of the constituent 

 parts of the cells were being gradually elucidated, it became recog- 

 nised that the cell-substances themselves were not composed of 



