DYNAMICS OF THE POINT OF NO RETURN DURING 

 DIFFERENTIATION IN BLASTOCLADIELLA 

 EMERSONII 



Edward C. Cantino 



Department of Botany, Michigan State University, 

 East Lansing, Michigan 



I left East Lansing a few days ago knowing 

 that cell differentiation and morphogenesis were 

 riddles which had served admirably for many 

 years as focal points for honorable speculation. 

 I will leave Penn State, today, with the strong 

 suspicion that solutions to these problems are 

 far from just around the corner. 1 trust, there- 

 fore, that I will be forgiven if, during the short 

 time we have left this morning, I add some haze 

 of my own to this generally smoggy area. 



Almost twenty years ago, in a fresh-water 

 pond behind old MacFarlane Hall on the campus 

 of the University of Pennsylvania, 1 discovered, 

 isolated in pure culture, and subsequently chris- 

 tened as a new species, the Phycomycete known 

 as Blastocladiella emersonii 1 put this specific 

 epithet upon it because of fond memories of my 

 first real teacher. Professor Ralph Emerson, 

 who but a few years before had introduced me 

 to the fascinating antics of these ubiquitous 

 aquatic fungi commonly known among mycolo- 

 gists as the water molds. 



I shall spend perhaps half of my time, this 

 morning, developing Blastocladiella' s back- 

 ground. This will serve a dual purpose, because 

 Dr. Lovett, who follows me on the program, will 

 also be discussing his studies of B, emersonii. 

 Let me begin, therefore, by showing you more or 

 less what 1 saw in 1948 when 1 took the first 

 spore of B. emersonii ever to be rendered cap- 

 tive and put it on a slab of nutrient agar medium 

 in a Petri dish (Fig. 1). The spore germinated 

 and developed into a little plant with root-like 

 rhizoids. At maturity, almost (but not quite) all 

 of this thallus was converted into a spore-bear- 

 ing sac, the sporangium. The first figure shows 

 a cross section through a spore sac in which 

 the protoplast has been cleaved up into spores. 



Subsequently, these spores were liberated 

 through exit pores in the sporangia! wall and 

 settled on the surface of the agar immediately 

 around the parent plant. The latter, thus depleted 

 of its protoplasm and now an empty shell, col- 

 lapsed. The newly liberated spores, however, 



SPORE 



J- 



FIRST GEN 

 DC CELL 



FIRST GEN 

 SPORES 



^ 



CLONE OF 

 2 ND. GEN CELLS 



(1) DC CELL WITH 3 RD 

 GEN IN SITU 



(2) 00 CELL, NON VIABLE 



(3) OC CELL DISCHARGING 

 3RD. GEN , 5 X VIABLE 



(4) OC CELL DISCHARGING 

 3RD. GEN, % VIABLE 



(5) 00 CELL DISCHARGING 

 3 RD. GEN, 100% VIABLE 



(6) ORANGE CELL 



(7) BROWN RS CELL 



Fig. 1. 



Schematic representation of the totlpotency of 2nd and 

 3rd generation clones derived from a single spore of 



Blastocladiella emersonii. 



149 



