ROUND TABLE DISCUSSION 217 



there is less resistance to cold there is less tendency to the 

 breaking of the plasmodesma. 



Lees: It depends on what you regard as the critical locus. The 

 organ systems controlHng diapause in insect eggs, larvae and 

 pupae are different. However, although diapause mechanisms, 

 even in closely related species, have probably been evolved 

 independently, natural selection has had to act on existing 

 growth-controlling systems, such as the endocrine system. 

 Therefore a certain uniformity emerges when the mechanisms of 

 particular stages are compared. Some further similarities, 

 especially in connection with respiratory metabolism, appear 

 if the reacting tissues are regarded as the critical locus. 



Halvorson: In micro-organisms, those most resistant to the 

 environment are spherical. Spores, too are all more or less 

 spherical. I do not know though whether this is in any way 

 significant. 



Moderator: It might be rewarding to focus our discussion 

 upon the surface of the dormant organism. Is it not true that 

 such a surface is generally waxy or at any rate hydrophobic? 



Lees: Well, as most insects possess a waterproof cuticle 

 throughout development one would have to find out whether 

 the waterproofing was more efficient during diapause. I do not 

 think that this has yet been studied critically. It is perhaps worth 

 mentioning, however, that silkworm pupae show a visible 

 accumulation of wax after they have remained dormant for a 

 year or two. 



Wahl: a morphological feature common to many fungi in 

 the dormant stage is the thick wall which reduces penetration. 



Halvorson : It is true that spore cell walls are different from 

 the vegetative cell walls. It is also probably true that Gram 

 positive organisms, which are more resistant have a cell wall 

 differing from that of the less resistant organisms. There may 

 be a correlation between the type and composition of the cell 

 wall and the dormancy and resistance of the cell. 



