306 CELL HEREDITY 



This organism consists of a basal rhizoid in which the nucleus resides, 

 a narrow stalk some 4 to 6 centimeters long, and a terminal cap of dis- 

 tinctive morphologv which differs from species to species. By cutting 

 the stalk, one obtains nucleated and anucleated portions. Hammerling 

 studied the regenerative capacities of the.se fragments, and he made inter- 

 species graft hybrids with them. He found that segments of anucleated 

 stalk were capable of regnerating new caps for a limited period, but 

 that onlv nucleated regions could continue to do so repeatedly and in- 

 definitelw Apparently, morphogenetic activity was retained by 

 anucleated regions for a considerable time but, eventually, nuclear 

 activity was required. In graft hybrids, as shown schematically in 

 Figure 11.1, cap morphology was eventually determined by the nucleus, 

 and if nuclei of both species were present, the cap form was intermediate. 



These studies are of great interest as a pioneering attempt, and .serve 

 to illuminate some of the difficulties of the problem. The distinction 

 between nucleate and anucleate involves far too many parameters to pro- 

 vide much analytical power. Similarly, the dichotomy between nuclear 

 and cytoplasmic function does not help us very much; consider simply 

 that the nucleus contains not only the chromosomes but also the 

 nucleolus and the nuclear membrane, the outer layer of which is coated 

 with cytoplasmic particles (ribosomes). This level of analysis is too 

 general: more incisive methods are needed for a more penetrating 

 analysis. 



It is not an easy matter to study integrative mechanisms, which are, 

 by their very nature, subject to disruption in the process of their 

 analysis. Nevertheless, the investigation of biochemical pathways of 

 synthesis of the macromolecular nucleic acids and proteins, as well as 

 the cytochemical localization of these processes in specific regions and 

 organelles of the cell, is providing an essential framework. 



This chapter might appropriately be subtitled, "Life Among the 

 Macromolecules,' for the central focus of interest is upon genetic 

 mechanisms controlling the formation and activity of the nucleic acids 

 and proteins. Within the limits of our present understanding, cell inte- 

 gration at the molecular level may be thought of in terms of specificity 

 and timing of synthesis of these macromolecules. On the simplest view, 

 all other cellular features may be derived from these. 



This formulation totally omits the question of whether subcellular 

 structures, such as chloroplasts, mitochondria, and kinetosomes, are 

 copied on a supertemplate in which structural specificity is conserved 

 during replication in some novel manner. The information available on 

 this problem has been summarized in Chapter 9. In this chapter, we 



