ACTIVITIES OF THE CLUB 81 



use of different biological materials : Engelmann — purple sulfur bacteria ; Molisch — 

 purple non-sulfur bacteria ; Winogradsky — colorless sulfur bacteria. Buder at- 

 tempted to harmonize the diverse views by categorizing the organisms employed. 

 The existence of an intimate connection between the photosynthetic activity of the 

 purple sulfur bacteria and their respiratory phenomena was first clearly expressed 

 by Kluyver and Donker. 



Van Niel demonstrated conclusively the photosynthetic nature of the metabolism 

 of the purple sulfur bacteria by devising methods for growing them in pure culture 

 in strictly mineral media in the light. His data show that the photosynthetic carbon 

 dioxide utilization depends quantitatively on the oxidation of sulfide and sulfur. He 

 also disclosed a similar relationship for the green sulfur bacteria. Comparing these 

 photosyntheses with that of the green plant, van Neil formulated the hypothesis 

 that the several photosynthetic reactions are all examples of photochemical carbon 

 dioxide reduction with a different hydrogen donor in each case. This generalized 

 view of photosynthesis made possible the explanation of the photosynthesis of the 

 non-sulfur purple bacteria as one in which the normal inorganic hydrogen donors 

 for the reduction of carbon dioxide are replaced by organic molecules. A variety of 

 indirect and direct experimental evidence has substantiated this interpretation. 



Critical evaluation of the objections to the generalized concept of photosynthesis 

 leaves unimpaired the viewpoint that photosynthesis is a photochemical carbon 

 dioxide reduction in which organic compounds as well as inorganic substances or 

 even molecular hydrogen can play the role of hydrogen donors. 



The consequence of the acceptance of this broad generalization is that it renders 

 untenable the classical Willstatter-StoU theory of green plant photosynthesis. 



After discussion of both papers, the meeting adjourned at 4:35 p.m., to be continued 



over the inviting tea and refreshments served by friends at the Garden. 



Honor M. Hollinghurst, Recording Secretary. 



March 2. Meeting in Schermerhorn Extension, Columbia University. 



The meeting was called to order at 8:15 p.m. by Dr. Lela V. Barton, the second 

 Vice-President. Despite the promise of a five siren air raid drill, 17 members attended. 

 The minutes of the preceding meeting were approved. The scientific program was pre- 

 sented by Dr. Ray F. Dawson who spoke on "Some Aspects of Parasitism in the 

 Mycorrhizae of Shortleaf Pine." 



The fungus or fungi which induce mycorrhiza formation on the roots of shortleaf 

 pine in the Missouri Ozarks area are apparently obligate parasites. The nature of 

 the symbiotic relationship between fungus and tree roots is determined largely by 

 environmental factors. When the trees are grown upon soils which are nutritionally 

 poor or unbalanced or when light intensity is low, fungal invasion of the short roots 

 readily occurs, and many well developed mycorrhizae are formed. Tree growth may 

 vary from slow to negligible. When the trees are grown upon fertile soil mycorrhiza 

 formation is difficult and slow and tree growth may be good, but if the soil contains 

 appreciable amounts of organic matter the seedlings w-ill most likey fall victim of 

 damping-off fungi. When the trees are grown upon soils which contain relatively 

 low amounts of the necessary nutrients but when these nutrients are present in 

 physiologically balanced proportions on the soil colloids mycorrhizal development 

 and tree growth are both favored. Under such circumstances the mechanism of the 

 beneficial effect of mycorrhizae upon tree growth seems to be associated with an 

 increased salt absorption which is conditioned by an increased rate of aerobic respira- 

 tion and by a newly introduced mechanism for anaerobic respiration both of which 

 serve to maintain the energy output necessary for the growth processes. Hydrogen 

 ion excretion by the roots under such circumstances is increased several times thus 

 making it possible for the root colloids to undergo more intensively base exchange 

 reactions with the soil colloids in the initial phase of salt absorption. The enhanced 

 absorption of salts may then bring about greater water absorption and resulting in- 

 creases in both volume and mass of the plant tissues. 

 Following the discussion period, the meeting adjourned at 9:35 p.m. 



Honor M. Hollinghurst, Recording Secretary. 



