72 The Structure of Protoplasm 



Perhaps it will clarify matters somewhat if we start with the raw 

 materials available to the plant and attempt to trace, in a general 

 way, their formation into larger aggregates. Inorganic ions and water 

 molecules are brought into the plant where carbon atoms from car- 

 bon dioxide have already been bound together into short carbon 

 chains with hydrogens and oxygens attached, as in glucose. These 

 we may think of as the basic substances. They are not combined at 

 random to form various substances, but instead are brought into the 

 presence of an already existing protoplasm, where only particular 

 constructions are permissible. The protoplasm present is a "going 

 concern" consisting of mechanisms which are capable of converting 

 these raw materials into particular molecular structures. We now 

 become confronted with the matter of construction, or shall we call 

 it synthesis. But synthesis of what, of more protoplasm, in place, 

 from basic materials, a sort of accretion; or of more mechanisms 

 similar to those already existing as component structures of the pro- 

 toplasm; or synthesis of large molecules, as those of protein, which 

 we may think of as building blocks used for construction of the 

 mechanisms? In other words, where does chance, as exemplified by 

 random interaction, enter into the formation of new protoplasm, and 

 at what stage does the pattern of pre-existing materials cease to be 

 of significance? 



We are rather rapidly heading towards a dynamic picture, yet it 

 is the static, or only a single frame from a movie film, with which 

 we would momentarily be satisfied. If we should discover that it is 

 the larger molecules which are synthesized, then we have the task 

 of finding how they are put together to form a mechanism; and when 

 we know that, we still have to discover the organized arrangement 

 of the mechanisms which will produce active protoplasm. We have 

 omitted to mention synthesis of smaller molecules of which the larger 

 seem to be composed. The queries come up, which we repeat 

 although difficult to formulate clearly, as to whether the new proto- 

 plasm is built up by accretion in situ from the basic small-molecule 

 materials, or by addition of large already-elaborated molecules to 

 the existing protoplasmic structures, or by bringing already-built 

 mechanisms into proper relations for protoplasmic activity. The 

 difficulty of merely stating the questions is probably evident. 



Many additional queries arise concerning "mechanisms," the 

 simplest of which may be the respiration complex which we have 

 just considered in a general way. Here the nature of the complex is 

 not yet well established, although small molecular mechanisms, en- 



