ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 525 



on the under surface. They are also very numerous on the upper 

 part of the stem, where they are also protected by glandular hairs. 



Properties and Mode of Formation of Duramen.*— J. Gauners- 

 dorfer gives an historical resume of what is known respecting the 

 duramen, which is distinguished by frequently containing gummy 

 and resinous substances in its vessels or cells, as well as large 

 deposits of carbonate of lime. His own observations he sums up as 

 follows : — 



The production of duramen takes place in consequence of the 

 elements of the wood becoming filled by derivatives of the solid 

 woody substance ; these products being formed to some extent in the 

 part which becomes indurated, and partly in neighbouring portions 

 of the wood ; by this means the extent of duramen is increased. 

 These substances must originally be fluid and rich in tannin ; but 

 the cells contain also other substances which give to the duramen 

 its great power of resistance. Nitric acid or "macerating fluid," 

 and then potash- or soda-ley, remove most of these substances, 

 except in the case of Diospyros. If the induration is carried on suffi- 

 ciently long, the cell-walls are also partially destroyed, and the pro- 

 ducts of decomposition mingled with the contents. The composition 

 of the substances contained in the duramen varies with the species ; 

 that of the Amygdaleas, for example, contains gum (?), of the coniferse 

 resin, of Syringa resinous substances. The purpose of the duramen, 

 at least in the lower parts of the branches, is to furnish a protection 

 for the sound wood against the influence of atmospheric agents. 



History of Assimilation and of the Functions of Chlorophyll, t— 

 A. Hansen gives a list of the researches and conclusions on this 

 subject from the days of Ingenhousz, Senebier, and Hales. The first 

 scientific explanation of the phenomena he considers to be that of 

 Sachs, between the years 1862 and 1865, that the starch in the 

 chlorophyll-grains is a product of the living chlorophyll, and is pro- 

 duced in the chlorophyll by its power of assimilation. The author 

 criticizes unfavourably the views of Pringsheim with regard to the 

 nature, mode of formation, and functions of hypochlorin. 



Theoretical View of the Process of Assimilation. J — In his 

 investigations on the chemical constitution of protoplasm,§ J. Eeinke 

 was led to frame a hypothesis as to the immediate products of the 

 reduction of carbonic acid. He points out that this gas, C0 3 H 2 , may 

 be subjected to three degrees of deoxidation. By the removal of one 

 combining proportion of oxygen it becomes formic acid, C0 2 H 2 , which 

 he states is always formed in every vegetable cell. The second stage 

 of deoxidation reduces it to formic aldehyde, COH 2 , a remarkably 



* SB. K. Akad. Wiss. Wien, Ixxxv. (1882). See Bot. Centralbl., x. (1882) 

 p. 163. 



t Hansen, A., ' Gesehichte der Assimilation u. ChlorophyHfunction,' 90 pp. 

 Leipzig, 1882. Also Arbeit Bot. Inst. Wurzburg, ii. (1882) pp. 537-626. 

 % Bot. Ztg., xl. (1882) pp. 289-97, 305-14. 

 § See this journal, ante, pp. 361-2. 



