Viii PREFACE 



of the Plant Tumor Cell," by Armin C. Braun, tlie Rockefeller Institute; 

 and "Regeneration in Vertebrates: The Role of the Wound Epithelium," 

 by Marcus Singer and Miriam Salpeter, Cornell University. 



Moscona discussed the ability of dissociated cells to aggregate to 

 form tissues and organs. He demonstrated clearly the existence of con- 

 sistent patterns of aggregation for various types of cells and, in addi- 

 tion, showed the dependency of cell-aggregation patterns on the age of 

 the tissue and on temperature. Moscona also indicated that one of the 

 main prerequisites of cell aggregation is a cellular product of mucoidal 

 nature, much like intercellular ground substance. 



Sussman described his work with the slime mold myxamoebae, a 

 typical unicellular organism. When growth of the indi\idual slime 

 mold cell ceases, individual cells collect in multicellular aggregates. 

 Sussman described the patterns of aggregation and postulated the exist- 

 ence of two types of cells during the unicellular part of a mold's 

 existence. He further suggested the function of each of these two types 

 of cells in the pattern of cell aggregation. 



Brachet discussed the role of ribonucleic acid and sulfhydril groups 

 in the growth and differentiation of the embryo. Noting that ribonu- 

 cleic acid is definitely involved in the synthesis of specific proteins, he 

 raised the question as to what inducing substance or evocator stimu- 

 lates morphogenesis. Brachet's studies show that the distribution and 

 concentration of ribonucleic acid correlate highly with morphogenesis 

 in the embryo. There is still no clear evidence, however, that ribo- 

 nucleic acid is the only significant constituent of the ribonucleoprotein 

 particle. In addition, Brachet pointed out the importance of the sulfhy- 

 dril group in morphogenesis, discussed the utilization of sulfhydril 

 reagent in current research, and emphasized the need for more work in 

 this important area. 



Wardlaw demonstrated in his paper the extreme range of floral 

 types and morphogenetic patterns encountered in the angiosperms. 

 He showed that information already at hand makes it possible to unify 

 and simplify the theories of the inception and development of flower- 

 ing, and he discussed some of the problems for which solution is still 

 required. Braun examined the question of what fundamental changes 

 occur in the onset of plant tumors. He suggested that the change from 

 the normal to the neoplastic condition involves a return from the nor- 

 mal precisely directed plant metabolism to a more "primitive type" of 

 metabolism, but he noted that this change appears to be a perfectly 

 reversible one. Reversal from tumorous to normal metabolism appar- 

 ently results from reimposition of a restraint on particular metabolic 

 areas of the "primitive" neoplastic cell type. 



Singer's thesis was that during the healing process epidermis serves 

 ( 1 ) to remove debris ( cellular, particulate, and molecularly-disbursed 



