80 T O R R E Y A 



program was Dr. Frances E. A\'ynne who spoke on "Variability and Distribution of 

 Drcpanocladiis in Xorth America." 



Drepanocladiis, like many aquatic and semi-aquatic plants, is extremely variable. 

 Field and herbarium studies have been made to determine which variations are 

 hereditary and which are merely environmental fluctuations. Careful examination of 

 leaves from different parts of the same plant shows that elongated leaves, costae, 

 and cells are always produced when the plant grows submerged in water, whereas 

 shorter leaves and cells are produced by stems which grow emergent. Many of the 

 described varieties are merely seasonal phases produced by changes in the water 

 level. The present monographic study has reduced the previously recognized 24 spe- 

 cies and 30 varieties to 9 species, 1 subspecies, and 4 varieties. Hereditary factors 

 determine the presence of an excurrent costa and secund leaves ; therefore these 

 characters are used as the basis for varieties in several species. The environmental 

 fluctuations of the shape of the leaves, costae, and cells are not given taxonomic 

 recognition. 



The species of Drcpaywcladus may be classified geographically into two groups — - 

 arctic-alpine and boreal-montane. The arctic-alpine species are restricted in their 

 range to the arctic regions ; the boreal-montane species are widespread in the arctic 

 but occur also in boreal and mountain bogs and swamps. 



The species of Drepanocladiis may be divided into two categories on the basis 

 of fundamental variability. All the boreal-montane are extremely adaptable and 

 variable and as a result of their toleration of a large variety of habitats have spread 

 over a wide range. The arctic-alpine species are stable, clear-cut species limited to 

 one region and one type of habitat. 



Drepanocladiis has a circumpolar distribution in both hemispheres. In Xorth 

 America its present range coincides with the maximum extent of continental and 

 cordilleran glaciation during the Pleistocene. In eastern Xorth America the distribu- 

 tion in partially glaciated states such as Pennsylvania, X'ew Jersey, Ohio, Indiana, 

 and ^Missouri is significant. In these states Drepanocladiis does not occur south of 

 the till sheets except in a few isolated stations. In western Xorth America it is found 

 in mountain bogs and alpine meadows. 



Four types of localities may have provided refuges for plants such as Drepanoc- 

 ladiis during the Pleistocene: (1) areas south of the Pleistocene ice (2) arctic areas 

 north of the ice (3) unglaciated lowlands and (4) mountains or nunataks. 



Two types of distribution result from the Pleistocene glaciation: (1) relic, static 

 and (2) general, widespread. Any hypothesis, proposed to explain the xx)st-Pleisto- 

 cene dispersal of plants, must consider these two tj'pes of distribution found on 

 glaciated areas. Of the numerous explanations which have been proposed, the most 

 satisfactory is founded on the genetic constitution of the plants. Species may be 

 plastic and adaptable or rigid and static. The boreal-montane species of Drepanoc- 

 ladiis are adaptable because a large number of individuals survived the Pleistocene 

 in a large variety of habitats -on all of the possible refuges ; therefore a large number 

 of biotypes contributed to these plastic species. The arctic-alpine species are rigid 

 because only a few individuals survived in a few habitats on only one of the refuges ; 

 the biotypes contributing to these species were depleted by the vicissitudes of the 

 ice age leaving the species genetically rigid. 



The second speaker was Dr. ]Morris Winokur who spoke on '"Photosynthesis in Bac- 

 teria." 



The attempt to interpret the metabolism of the green and sulfur bacteria has 

 resulted in the development of a generalized concept of photosynthesis which is 

 applicable to the green plant as well. 



At the beginning of the twentieth century, there existed three conflicting theories 

 concerning the physiology of the purple bacteria. Engelmann believed that the purple 

 bacteria were able to photosynthesize much in the manner of the algae. W'inograd'sky 

 postulated that the oxidation of hydrogen sulfide and sulfur represented a substitute 

 for the respiration of organic substances, characteristic of the normal functioning of 

 most organisms. Molisch developed the thesis that the purple bacteria cannot assimi- 

 late carbon dioxide, but they assimilate organic compounds in the light. The contro- 

 versial nature of the results obtained bv these three investigators was due to their 



