5 o PHYSIOLOGICAL MORPHOLOGY 



the general considerations given in Sect. 5, with which each and every hypothesis 

 must agree. 



[It is hardly conceivable that each pangen or physiological unit could possess 

 one specific kind of irritability only, and if pangens have inherent in them all the 

 general irritabilities which characterize the protoplast as a whole, the assump- 

 tion of these hypothetical units brings us no nearer a comprehension of the vital 

 mechanism. It is possible, however, that different pangens might have certain 

 irritabilities more highly developed than others, and the specific irritability of 

 a sensitive organ might be due to the preponderance of one special kind of pangen, 

 or to the combination of several different kinds. ED.] 



SECTION 9. Relations between the Nucleus and Cytoplasma. 



In the protoplast, as in every organism, the course of events is 

 determined by the interactions of its component parts, which mutually 

 support one another and are mutually interdependent. For the correct 

 determination of these internal protoplastic relationships, the same general 

 rules are applicable as were given in Sect. 6. 



It is comparatively easy to discover the function of an organ such 

 as a chloroplast, which subserves mainly one particular purpose ; but 

 it is extremely difficult to make out all the manifold relations of nucleus 

 and cytoplasm, upon the maintenance of which the life of the protoplast 

 depends. Though a comprehensive grasp of the inherent character of these 

 relationships has not yet been attained, still a general indication of the 

 questions at issue may be profitable, especially as a clear realization of 

 the meaning of the phenomena observed is, in many cases, conspicuously 

 wanting. 



Since it is the co-existence of nucleus and cytoplasm which constitutes 

 the protoplast, the latter ceases to exist as such when its component parts 

 are separated from one another, just as a lichen, formed by the symbiotic 

 union of an alga and a fungus, is no longer a lichen when its two con- 

 stituents are cultivated apart from one another. The comparison is none 

 the less accurate because in the latter case the component parts are dis- 

 tinct organisms capable of separate existence. Nor is it necessary that all 

 symbiotic organisms should be capable of cultivation when isolated from 

 one another. 



When an organism is transferred from favourable conditions to such 

 as render its continued existence impossible, its vital activity gradually 

 decreases, and death unavoidably supervenes, although until it dies 

 indications of functional activity are still perceptible. This is also the 

 case in separated organs which are incapable of continued existence when 

 isolated. Thus a muscle removed from the body is for a time still capable 

 of contraction (Sect. 52) ; an isolated chlorophyll body may continue for 



