638 STIMULUS-TRANSMITTING SYSTEM 



different kinds of stimuli, or whether a division of labour prevails in this 

 respect among the various protoplasmic connections which link up 

 adjoining protoplasts, must, of course, remain an unsolved problem for the 

 present. On the other hand, the question as to whether the proto- 

 plasmic connections serve for the conduction of different stimuli in 

 different tissues, is open to experimental investigation. 



The fact that protoplasmic connecting threads serve for the trans- 

 mission of stimuli, does not exclude the possibility that these structures 

 may in certain cases be partly or entirely engaged in translocation of 

 plastic materials. As a matter of fact, protoplasmic connections were 

 first discovered in the storage-tissues of certain endosperms, where they 

 are often very well differentiated ; in such cases it is quite possible 

 that they are principally concerned with translocation. 



B. INTRACELLULAR TRANSMISSION. 



Even if the protoplasmic connecting threads are regarded as the 

 intercellular stimulus-transmitting paths, it is still necessary to account 

 for the transmission within the individual protoplast. A 'priori several 

 possibilities suggest themselves in this connection. In the first place, 

 it is conceivable that the entire protoplast is endowed with the 

 capacity for conducting stimuli ; secondly, the faculty in question might 

 be restricted to the ectoplast ; finally, special fibrillar structures might 

 be developed for the purpose. The last-mentioned possibility has been 

 recently discussed at length by Nemec. 339 Max Schulze, Apathy, Bethe 

 and others have shown that the nervous tissue of animals contains a 

 system of delicate fibrillae, which are regarded by these investigators as 

 the actual paths of transmission, on account of their unbroken continuity, 

 and for other reasons. Starting from the observations and conclusions 

 of the aforesaid animal physiologists, Nemec succeeded in finding very 

 remarkable fibrillar structures in the root-tips of a variety of plants 

 (Allium Cepa, Hyacinthus orientalis, Iris germanica, Cncurbita, Pimm, 

 Aspidium, etc.), more particularly in those rows of plerome-cells which 

 later become converted into hadrome- vessels. The elements in question 

 are traversed by longitudinal protoplasmic strands, which extend from 

 one end of the cell to the other, and which correspond on the opposite 

 sides of each transverse wall. In stained microtome-sections of suitably 

 fixed material, and sometimes even in the living condition (Allium Cepa), 

 these strands display a distinct fibrillar structure. The fibrillae form a 

 reticulum, which, as already explained, extends from one transverse 

 septum to the next. They do not, however, traverse the walls, nor are 

 they anywhere continuous with protoplasmic connections ; the fibrillar 

 systems of different cells are thus not directly connected with one 

 another. This circumstance alone throws grave doubts upon the validity 



