74 The Structure of Protoplasyn 



molecules and placing them in an orderly manner to form the starch 

 grain. It seems probable that, in detail, there are many small mechan- 

 isms within the plastid which are active in placing the glucose mole- 

 cules on the surface of the grain and also in producing an ether link- 

 age between them. Actually we know only that the starch grain 

 becomes larger; to our mechanistic minds there must be machinery of 

 some sort, but of its construction we know very little. In the plastid 

 we think of an orderliness of some sort, in the placement of the ma- 

 chinery which produces starch grains, since the shapes of the starch 

 grains are fairly specific with plant species, and as a matter of fact, 

 the behavior of the starch itself is in some respects almost as specific 

 as the structures of the grains. Despite this, it seems fairly reasonable 

 to think that the individual mechanisms which bring about the con- 

 densation of glucose to starch are more or less universal in plants. 



From the biological point of view we think of the plastid as a very 

 large particle. Shall we think of its growth as consisting of a build- 

 ing-up process, in place, from small molecules, or large molecules as 

 of protein, or from ready-made small mechanisms? We come to 

 similar questions concerning a large protein molecule of some thou- 

 sand atoms. Is there a machine to manufacture these with the proper 

 amount of amino acids for each species and for each mechanism 

 where several specific proteins are apparently needed as in respira- 

 tion? Or is it more likely that the protein molecules are merely the 

 wreckage of the larger mechanism complexes which were built by 

 accretion of the small basic molecules? Questions of this sort and 

 the discussion of them leads primarily to a demand for experimental 

 answers, and each small point is likely to mean a large experimental 

 task. 



Concerning these questions which have been posed here, there is 

 undoubtedly much more information in the literature than is known 

 to any one of us. Some of it is based on cytology or allied subjects; 

 some on morphological, some on physiological and some on other bio- 

 logical procedures. Here and there are items in chemical and phys- 

 ical journals. Our questions involve the interpretation of biological 

 experiments from a physical and chemical point of view; for example, 

 the microscopic measurement of the rate of deposition of a growing 

 cell wall, the transverse septum of an algal cell (121) . This is a bio- 

 logical experiment, yet the interpretation of these measurements 

 into the rate of deposition of glucose molecules is chemical in that 

 it gives a rate of ether linkage formation, and physical in that the 

 process of crystal formation may be studied. 



