222 



CYTOLOGY 



modern? Consult a textbook if neces- 

 sary. 



7. To what modern term do the "ids" 

 most closely refer? 



Are the parental chromosomes present 

 in a hvbrid? What is the significance 

 of this? 



George A. Baitsell 



The Cell as a Structural Unit 



Reprinted with the permision of the author 

 and publisher from the American Naturalist 

 74:5-24, 1940. 



Year by year since 1828 when 

 Wohler synthesized urea in the labora- 

 tory and showed that organic chem- 

 istry, the chemistry of life, was merely 

 a greatly complicated inorganic chem- 

 istry, that the difference between the 

 compounds formed in the living organ- 

 ism and those existing outside the living 

 organism was not one of kind but of 

 degree of complexity, the boundary 

 wall between the chemistrv of life 

 and non-life has been repeatedlv shat- 

 tered. As a result it is now apparent 

 that the plan of organization exhibited 

 in the living world, with the cell as the 

 basic unit, does not differ intrinsically 

 from that exhibited by inorganic ma- 

 terials, but is a plan which has become 

 amazingly elaborated and of extreme 

 complexity. 



The phenomena characteristic of 



life are only possible when a tremen- 

 dously complex association of certain 

 elements is present. But the materials 

 used in the hfe stuff, protoplasm— the 

 atoms of carbon, hydrogen, nitrogen, 

 oxygen, sulfur, and various other ele- 

 ments — are the same in living materials 

 as elsewhere. Since even' clement has 

 its own unchanging characteristics, the 

 structure and behavior of a carbon 

 atom or the atom of anv other clement 

 is not changed when it is temporarily 

 built into the protoplasm of a living 

 organism. But the almost incompre- 

 hensible complexity of living materials, 

 constructed from a wide assortment of 

 elements, is accompanied by unique 

 phenomena maintained bv the ultiliza- 

 tion of radiant energ}' e.g. the character- 

 istics of the living state— which are be- 

 yond and different from those of the 



