ROUND TABLE DISCUSSION 219 



Finally, would you care to say whether cryptobiotic states 

 are a useful feature in evolution? 



SESSION II 



(V) The Selection of Suitable Biological Materials 



Moderator (Hestrin): A proper choice of biological material 

 for the examination of the problems of dormancy could no 

 doubt be a matter of critical importance for the advancement of 

 knowledge in this area. Could we perhaps arrive at some 

 agreement as to the kind of properties we would want in such 

 biological objects of our choice? Perhaps Prof. Halvorson who 

 has done so much of the pioneer work on this problem would 

 consent to give us his opinion as to the manner in which the 

 choice objects for studies should now be made? 



Halvorson: Little progress was made in the study of the 

 physiology of the bacterial spore until it was realized that proper 

 separation of the dormant stage (ordinary spore) was essential. 

 I am sure this is applicable to all the other fields. 



Moderator: I suppose heterogeneity in the bacterial spore 

 population might be a serious obstacle to quantitative studies 

 of the phenomena. Is it now possible to get synchronized 

 germination in homogeneous spore samples? 



Halvorson Jr. : I think that variations in time of germination 

 result from variations in time of storage of the spores. As 

 activated forms of spores show considerable loss of weight, we 

 have been able to perform separation by equilibrium sedimenta- 

 tion in the density gradient. Another heterogeneity was in 

 resistance to ethylene oxide resulting from phenotypic variation 

 in fat content against a constant genetic background. Here we 

 accomplished a separation by electrophoresis. Thus by use of 

 appropriate physical techniques one can get greater population 

 homogeneity. 



Kohn: Would density gradient centrifugation ensure homo- 

 geneity in spores? 



Halvorson Jr. : We know we can separate active spores from 



