Lecture XI — 157 — Theories 



supporters in Busich (1913) for asclepiads, and Kerkichu (1930) 

 and Stajanow (1916) for orchids. Stahl's idea in regard to orchids 

 was that the orchids can take in and transpire only a small amount 

 of water but the symbiotic fungi have a greater osmotic power and 

 the orchids owe to this property a greater inflow of water and the 

 salts dissolved therein. 



Objections to the Stahlian Hypothesis: — Opposition to Stahl's 

 view developed. Tubeuf (1903) pointed out that Stahl's view 

 could not apply to endotrophic mycorrhizae because, he said, there 

 is no connection of the endotrophic mycorrhiza with the surrounding 

 soil, meaning apparently that individual hyphae are insufficient to 

 meet the needs of the plant. Stahl was at fault, too, in regard to 

 liverworts; for Ncmec (1899) had asserted that Marchantiaceae, 

 being starch producers, could not have endophytes, which were to be 

 expected only with the sugar-producing Jungernianniaceae; and 

 Stahl had seized upon this suggestion as fitting into his hypothesis. 

 But actually, endophytes are commonly present in the Marchantiaceous 

 liverworts. Then, as to orchids, Fuchs & Ziegenspeck (1925) 

 pointed out that in orchid mycorrhizae the transformation of cortical 

 cells into digestion-cells interferes with water-transport, hence 

 lessened transpiration is not compensated by mycotrophy but is 

 rather caused by it. 



Opposition to Stahl's hypothesis developed also in regard to 

 his ideas in relation to soil sterilization. Existence of a struggle for 

 nutrient salts was posited amongst roots of all plants, and myco- 

 trophic plants were supposed to gain an advantage over concurrent 

 fungi through aid of mycotrophic fungi. The existence of such a 

 struggle was thought by Stahl to be demonstrated by the fact that 

 autotrophic plants do better in sterilized than in unsterilized soil. 

 But Neger (1903) conducted experiments that led him to conclude 

 that thriftier growth of plants in sterilized soil is to be attributed 

 mainly to the increase in nutrient salts caused by sterilization and 

 not (or only to a minor degree) to the misconceived battle against 

 soil fungi. 



Bjorkman's Hypothesis : — Coming still closer to an explanation 

 of mycotrophy, Bjorkman found a connection between the products 

 of photosynthesis in the host and mycorrhizal formation. A vigor- 

 ously growing plant in an environment moderately deficient in N and 

 P, or both, and exposed to optimum illumination forms abundant 

 mycorrhizae because there is abundant reserve of assimilate in the 

 root tissues for the mycorrhizal fungus to use. The author's only 



