800 AQUATIC PHYCOMYCETES 



5. Active growth, then active formation of oogonia: — 



(a) oogonia with antheridia : — in solution of leucin (0. 1 %) with tricalcium 



phosphate (0.1%). 

 {b) oogonia without antheridia: — in solution of haemoglobin (0.05- 



0.1%). 



6. Growth, then formation of sporangia, then of oogonia: — by placing the 

 mycelium in water from gelatin-meat extract; or by culture on dead insect in 

 water. 



7. Growth and simultaneous formation of sporangia and oogonia: — in 

 water with some fibrin or syntonin. 



8. Growth, then formation of oogonia and later sporangia: — after strong 

 nutrition of the mycelium transfer to 0.01 % haemoglobin. 



9. Active formation of gemmae: — by putting a well-nourished mycelium 

 in 0.6% tricalcium phosphate, or 1 % sodium chloride, etc. 



10. Growth with sporangia, then gemmae; or growth with oogonia, then 

 gemmae; or growth with sporangia and oogonia and then gemmae: — in the 

 items 3, 5 and 6 above, when the culture is continued to the complete exhaus- 

 tion of the nutrient material. 



General conclusions in regard to conditions for the formation of 

 sex organs are summarized as follows (Coker, Joe. cit., p. 566): 



1. In a mycelium which is constantly given fresh nourishment no oogonia 

 are ever formed. Young, just formed oogonia were, by means of fresh, soluble 

 food, induced to vegetative growth. The old were, however, killed. 



2. If a strongly nourished mycelium is changed to a medium of low nu- 

 tritive value (in which the formation of sporangia is rare or absent) oogonia 

 are formed in a few days. 



3. In a good soluble food, preferably at such concentration that the spo- 

 rangia cannot be formed, the mycelium begins to form oogonia as soon as the 

 solution is chemically changed on account of its growth, and has lost its 

 nutritive value. 



4. The formation of oogonia is particularly encouraged through phosphate, 

 which is likewise necessary to the formation of the antheridia. In a soluble food 

 that is poor in phosphate oogonia are formed, but no antheridia ; particularly 

 abundant are such oogonia in a pure solution of haemoglobin. 



5. In many soluble foods, for example in peptone, gelatine, etc. are excret- 

 ed certain products of assimilation of the mycelium which hinder the 

 formation of oogonia. 



Since the work of the early investigators on the physiology of the 

 Saprolegniales, numerous modern studies concerning this aspect have 

 been made on members of the group. References to most of them are 

 given by Cantino (1950, 1955). 



