have to invoke long-term messengers. We do 

 not know what the papilla is composed of, but it 

 looks as though it might be a polysaccharide 

 of some kind. It may well be that some kind of 

 enzyme or enzymes are made that begin syn- 

 thesis long before one sees the morphological 

 event itself. We have no reason to say that 

 there couldn't be other kinds of RNA's having 

 other functions being made at the same time; 

 all we can point to is the observable event. 



We consider this to be interesting pre- 

 liminary evidence and it is the kind of problem 

 we want to pursue with our system. We would 

 particularly like to be able to characterize 

 some of the RNA's we think might be produced. 

 This, I'm sorry to say, just about summarizes 

 all we know about spore diffferentiation. 



Our information on spore germination is 

 even less definitive. Because of some interesting 

 parallels with the work discussed by Dr. Gross 

 on the first day (9) I would like to mention this 

 in an informal way. The next few plates will 

 show several stages during the germination of 

 the spore - a transformation fully as dramatic 

 as the differentiation of the spores themselves. 

 The next slide (refer back to Fig. 2) is just to 

 refresh your memory with regard to the orga- 

 nization of the spore with its nuclear cap and 

 the large mitochondrion, which, in certain sec- 

 tions, extends well up toward the anterior end 

 of the cell. Germination occurs quite rapidly 

 under our conditions and the next electron 

 micrograph (Fig. 19) shows the first stage we 

 have been able to catch. The spore is rounded 

 up; it no longer has the very thin, delicate outer 

 membrane and already looks as though it is 

 beginning to form wall material. It has retracted 

 the flagellum, and in this micrograph you can 

 see a longitudinal section of the flagellum within 

 the cell. The mitochondrium, instead of being 

 localized as before, is in several parts of the 

 cell and appears as more than one. All these 

 events occur in a matter of a few minutes. Even 

 at this early stage, there are points where the 

 originally continuous nuclear cap membrane 

 has become discontinuous. We do not know how 

 it occurs, but the ribosomes are beginning to 

 "leak out". Perhaps this is not the right term, 

 but that is exactly how it appears. 



Figure 20 is a section of a cell a few min- 

 utes later during germination. It is now a little 

 round cyst with the ribosomes spread through- 

 out the cell and no sign of a nuclear cap. There 

 is the nucleus, a mitochondrion, which we think 

 may actually have divided by this time, and a 

 few of the granules from the zoospore. This cell 



Fig. 19. 



An electron micrograph of an early stage in germination 

 to show the retracted flagellum and the beginning of nu- 

 clear cap disorganization. 



Fig. 20. 



A very young stage to illustrate the complete dispersal 

 of the cap ribosomes and initiation of the primary rhizoid 

 (r). 



175 



