62 PHYSIOLOGICAL MORPHOLOGY 



by the protoplast, in spite of its unceasing internal changes, is directly- 

 due. In the vital mechanism, chemical changes are indissolubly connected 

 with physical changes of either form or energy, and thus chemical problems 

 are necessarily always involved in the phenomena of growth, movement, 

 and indeed all vital manifestations. The term 'constellation,' used with 

 reference to the aggregate of conditions regulating the vital mechanism, 

 includes both the chemical nature and relationships of the component 

 parts, as well as their structural organization and the way in which they 

 are combined together to build up the protoplast. It can hardly be 

 doubted that a difference in the character of the organism may be produced 

 either by a difference in the structure of the protoplast or its component 

 parts, or by a difference in the chemical nature of the latter, or by 

 a combination of chemical and structural differences. 



When different lichen forms arise from similar algae and fungi, we 

 have an example in which the component parts are chemically identical, 

 but differ in the way in which they are arranged. Similarly, if the 

 nucleus and cytoplasm of different plants could be combined together 

 the new protoplast would certainly resemble in properties neither of the 

 original protoplasts, nor would the nucleus or cytoplasm of the new com- 

 bination resemble those of the old combinations from which they were 

 derived, and with which they are chemically identical. 



On the other hand, it may with certainty be assumed that the nature 

 and properties of physiological units, as well as of the organs and elements 

 which are formed from them, are largely determined by the chemical 

 character of the component molecules. So that, if from one physiological 

 unit particular molecules could be removed and others substituted, the 

 special inherent characteristics of the unit in question would be altered. 



It is impossible at present to determine to what extent the peculiarities 

 of different organisms are due to differences in the chemical nature of the 

 component parts of the protoplast, and to what extent they are due to 

 differences in the protoplastic structure, or whether in all cases both 

 chemical and structural differences exist side by side. Frequently 

 differences in the chemical nature of different nuclei &c., may be 

 detected, but the methods at our disposal are inadequate to enable us 

 to recognize all the chemical differences which may exist between the 

 great variety of proteid substances that undoubtedly take part in the 

 formation of the protoplast. A very slight difference in constitution may 

 be of considerable physiological importance, since thereby the nutritive 

 value of a particular substance may be markedly altered. 



The same general principles would be applicable to protoplasts which 

 were not mainly built up of proteid substances, as are those found on 

 the Earth. We have no grounds for supposing that nothing of a vital 

 nature could possibly exist in the absence of all proteid materials, and 



