FUNDAMENTALS OF CYTOLOGY 



From this point onward cytology stood out more clearly as a distinct 

 field of study, and its own problems became more sharply defined. 

 Among these w^as the task of determining to what extent the protoplast 

 actually is "the unit of structure and function" as was claimed, a question 

 to which we shall revert in the next chapter. It was soon discovered 

 that many very small organisms have the structure of a single protoplast, 

 that gametes and spores are likewise single protoplasts, and that the 

 protoplast, w^hether constituting a whole organism or only a portion of 

 one, multiplies regularly by division (Fig. 2). These discoveries, 

 together with others that followed, made it clear that many kinds of 

 biological problems would have to be attacked directly or indirectly 



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Fig. 2. — Figures of division of Tradescantia niicro.sporocytes published by Wilhelm 

 Hofmeister in 1848. This was a quarter of a century before chromosomes, shown plainly 

 here, appeared prominently in biological literature and came to be recognized as indi- 

 vidualized nuclear units. 



through the cell unit. To the extent that such problems require this 

 approach, they are cytological. As a matter of fact, much of the signifi- 

 cant knowledge of the protoplast gained in recent years has developed 

 in connection with questions that did not at first arise within the field of 

 cytology itself. 



The Classic Period of Cytology. — The latter portion of the nineteenth 

 century Avitnessed striking advances in biology and the other sciences. 

 It has become customary to refer to the last quarter of the century as the 

 "classic period" of cytology because of its many fundamental discoveries. 

 Some of the principal accomplishments of this period are enumerated in 

 the following paragraphs. 



Much was learned concerning the structure of cells and nuclei, their 

 reproduction by division, and the behavior of their several components 

 during the various phases of cell activity. Special attention was focused 



