THE PROBLEM OF NEURON PATTERN 169 



other which shows the external morphological neuron 

 pattern, without being impressed by the resemblance 

 between the usual types of neuron pattern and those of 

 the multiaxial plants and multiaxial animals, such as 

 the hydroids. Many neuron patterns, for example, are 

 much like tree patterns, and different modifications of 

 neuron pattern are at least as clearly distinguishable as 

 the forms of different species of trees. Resemblances of 

 this sort do not necessarily signify identity or even 

 similarity of constitution in the individuals or proto- 

 plasms concerned, but I believe they do at least suggest 

 similarity in axiate pattern, i.e., in the relations of 

 physiological gradients in the different protoplasms. It 

 is difficult, in fact, not to believe that similarities so 

 striking as those between neuron pattern and tree 

 pattern, for example, mean something physiologically 

 as regards the relations between the constituent axes 

 and their integration into the whole individual. The 

 hereditary constitution of the protoplasms of neurons 

 and of trees is doubtless very different, and the environ- 

 mental factors to which the plant is reacting are obviously 

 in large part or wholly different from those to which 

 the neuron protoplasm reacts. Notwithstanding these 

 differences the physiological relations of the axial gradi- 

 ents in the two types of individual may be more or less 

 similar and may determine similar types of growth 

 pattern. 



THE POSSIBLE FACTORS CONCERNED IN THE AXIATION 



OF THE NEURON 



The axon is a highly specialized outgrowth whose chief 

 function is evidently conduction. It probably has little 

 or no direct nutritive relation with its environment 



