Chapter 18

In previous chapters we have set down, with some discrimination, the contributions to the record of structural aspects of morphogenesis in the watermolds. Only in passing have we touched upon the factors that trigger or modify the genetically dictated form these fungi may take. This and the following three chapters review the literature dealing with external and internal factors that influence reproductive morphogenetic expression in the Saprolegniaceae. Experimental exploration of the physiology of reproduction in the family began with the efforts of Klebs (1896, 1899, 1900). One principle -or dictum as Kauffman (1926) would have it -to emerge from Klebs’ (1896) thinking is a concept now taken for granted: living organisms are influenced by their structure, by the interaction among their parts, and by their external environment. Put another way (in light of later developing biological concepts) the potential form that an organism can express is controlled genetically but manipulated by internal and external forces. Underlying Klebs’ concept of reproduction is the idea that every species has certain potentialities leading toward its own unique nature. The particular chemical or physical conditions prevailing at any given time will dictate the form that species will assume (Pieters, 1915a; Kauffman, 1926). If this Klebsian concept is correct, a given species should express itself morphologically in precisely the same way each time it encounters a specific set of external and internal conditions, barring, of course, any genetic change. A second species subjected to these very same conditions would react in some fashion contrary to the first, and the differences would be discernible in the physical form of the two organisms. It follows that no two species of watermold should react in the same way to uniform conditions. Klebs (1899) pursued this view by experimenting with the influence of nutrition on the nature of reproduction in Saprolegnia mixta (=ferax). Thus, he established a foundation for the study of reproductive morphogenesis, but left a legacy of little if any analysis. In the study on Saprolegnia mixta, Klebs’ aim was to determine what chemical factors in the nutrient environment (and to a lesser extent what physical factors of incubation) incited or altered the various modes of reproduction that this species could exhibit. He presumably worked with bacteria-free cultures, propagating the fungus in a wide variety of chemical and natural compounds: peptone, gelatin, hemoglobin, asparagine, glutamine, oxalic and acetic acids, alkaloids, and various sugars and inorganic salts, among others. Pea broth was the basal medium, and even though Klebs added known quantitites of test substances to it, the culture fluid was still chemically undefined. The discrepancies later coming to light when investigators repeated his experiments certainly can be traced in part to his use of pea broth and other undefined additives such as peptone and meat extract. Klebs discovered that particular organic and inorganic compounds favored sexual or asexual reproduction while others did not. Phosphates (among other minerals) elicited a strong sexual response in Saprolegnia mixta, as did hemoglobin and