Environmental and genetic control of differentiation in Neurospora 



and although it might ultimately be possible to work out the biochemical genetics of 

 this process in some detail, the system is certainly not an attractive one. 



This leaves the formation of protoperithecia as the third alternative which may be 

 suitable for our problem. The formation of these bodies on haploid mycelia is not a 

 very common phenomenon in the fungi, and it is most fortunate that Neurospora 

 belongs to the group of Pyrenomycetes which have them. They had already been 

 reported in the classical paper by Shear and Dodge (1927). However, their function 

 as female sex organs was first described by Dodge and Swift (1933) and by Dodge 

 (1935). Their development was later studied in some detail by Backus (1939). 

 Despite these investigations we are far from having sufficient information about 

 their detailed structure and development. 



Figure 2. The structure of a 

 protoperithecium o/Neurospora ; 

 asc: ascogonium ; r: receptive 

 hyphae (trichogyne) ; c: conidium 

 which fertilizes the receptive 

 hyphae. (From Backus, 1939.) 



When Neurospora is grown under suitable conditions to be defined later, the proto- 

 perithecia begin to develop in abundance after 3-4 days, and they can then be ferti- 

 lized. They are shown in Plate la; Figure 2 shows some details of their structure based 

 upon Backus's paper. We have made some preliminary investigations, trying to 

 follow the first steps in their differentiation. First, certain vegetative hyphae begin to 

 curve and form small spirals. These hyphae stain deeply with cotton blue. Next, 

 these spirals seem to attract hyphae from the surrounding mycelium, and the pri- 

 mordium (the ascogonium) becomes surrounded by dense balls of deeply staining 

 hyphae which after 3-4 days are easily recognizable under a low-power microscope. 

 The differentiation of these organs is thus a very well-defined and conspicuous 

 process which takes place within very few days, and which among the three possible 

 systems (growth type, formation of conidia, or protoperithecium formation) seems 

 to be by far the best suited for our purpose. 



173 



