196 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to assume a predetermined tint. From the experiments, M. "Weis con- 

 cludes that Oenothera biennis is a well-marked sun-plant, which in direct 

 solar light and at a temperature favourable to assimilation, assimilates 

 about three times as much carbon dioxide as in diffused light. On the 

 other hand, Polypodium vulgare assimilates with slightly more energy 

 in diffused light, and notably more than does Oenothera. Marchantia 

 •occupies an intermediate position between the other two plants. The 

 author points out that it would be interesting to conduct such a series 

 of experiments with the plants which fight for the light in our fields 

 and woods. 



Hydathodes in the Leaves of Woody Plants* — W. Edelstein has 

 investigated about seventy species of woody plants, and finds that 

 only in fourteen are hydathodes absent ; among the latter are Quercus 

 pedunculate, Q. Ilex, Rhamnus Frangula and cathartica, Spindle tree, 

 Ash, Acer platanoides, Beech, and Horse-chestnut. The structure of 

 the hydathode is as described by Haberlandt and others in herbaceous 

 plants. The physiological investigations were made with well-rooted 

 pot-plants, or cut branches with use of artificial pressure on the lines 

 employed by Moll. 



The author finds that cut branches, in the absence of any pressure, 

 retain the capacity of absorbing and excreting water for three to four 

 days without loss of intensity. In a series of experiments undertaken 

 to show how far the hydathodes shared in this process, the author 

 covered either all the leaves or only the hydathodes with vaselin, 

 albumin, or Cacao-butter. In neither case was any influence shown on 

 the absorption of water. The hydathodes were now removed by cutting 

 off the leaf-edges ; water-absorption went on as before, while great 

 drops of water appeared on the cut edges of the nerves. On the other 

 hand, absorption was almost completely stopped by etherising the 

 branch, and by removal of all the leaves. The author is unable to 

 explain the relation between absorption and excretion of water ; his 

 ■experiments show at any rate that absorption is not influenced by the 

 presence of the hydathodes. 



General. 



Ecologic Study of the Flora of Mountainous North Carolina.! — 

 J. W. Harshberger gives a detailed account of the factors determining the 

 character and the nature of affinities of the flora of this region. The 

 area embraces several mountain ridges with the associated valleys, the 

 former often attaining heights between 4000 ft. and 5000 ft. The effect 

 of the physiographic changes which have occurred in the history of the 

 geologic formation of the area on the distribution of the plants is dis- 

 cussed. Four kinds of plants, with reference to their phenologic distri- 

 bution, may be distinguished in the vegetation of the forests of eastern 

 North America, viz. — plants of boreal genera (Arctic, Hudson ian and 

 •Canadian species) ; plants of temperate genera (Alleghanian and Caro- 

 linian) ; plants of warmer temperate climate ; and neotropic genera. 



* Bull. Acad. Imp. Sci. St. Pt-tersb., xvii. (1902) pp. 59-64. 

 t Bot. Gazette, xxxvi. (1903) pp. 241-58. 



