92 SUMMARY OF CURRENT RESEARCHES RELATING TO 



portion of the petiole is, on the other hand, epinastic. The actual 

 movements of the leaf-stalk by which the different positions of the 

 lamina are brought about, consist either of curvature or of torsion, or of 

 a combination of the two, the movement being always in the direction of 

 least resistance. 



Phenomena of Curvature.* — Herr J. Wortmann replies to the 

 objections of Elfving to the explanation of the phenomena of geotropic 

 curvature advanced by him,! and reaffirms his previous conclusions. 

 The vertical elevation from a horizontal organ must be due, as de Vries's 

 plasmolytic experiments have shown, to unequal growth of the upper 

 and under side of the organ, and this must be the consequence of one of 

 two forces, or of a combination of the two — viz. unequal turgidity of the 

 two sides, and the unequal stretching of the membrane on the two sides. 

 De Vries supports the former theory, viz. that the geotropic curvature 

 is due to an accumulation of osmotic substances in the under side of the 

 organ. From experiments both on multicellular and on imicellular 

 organs like the sporangiophore of Phycomyces, Wortmann has come to 

 the opposite conclusion, that there is no evidence of any change in 

 turgidity, and therefore in osmotic force ; and that the geotropic curva- 

 tures both of unicellular and of multicellular growing organs are caused 

 by changes in the extensibility of the membranes, that of the under side 

 becoming greater when the geotropism is negative. This is, however, 

 not necessarily a mechanical stretching, but may be due to accumula- 

 tions of cellulose on the under side, and this again can be the result 

 only of movements in the protoplasm which cannot take place except in 

 living cells. 



(4) Chemical Chang-es (including' Respiration and Fermentation). 



Chemical process in Assimilation.^ — Di". T. Bokorny has made a 

 fresh series of experiments, the results of which he considers further 

 confirm the probability of Baeyer's hypothesis that the first product of 

 assimilation in plants is formic aldehyde. They were made in the light, 

 chiefly on cells of Sjpirogyra. He finds that, when carbon dioxide is 

 excluded, but mineral food-material supplied, green cells are able to 

 form starch out of methyl-alcohol and out of glycol, as well as out of 

 glycerin. 



Decomposition of Albumen in the absence of free oxygen.§ — From 

 a series of experiments made chiefly on Triticum vulgare and Vicia Faha, 

 Herr W. Palladin draws the following conclusions : — (1) If green plants 

 containing non-nitrogenous substances are j)laced in an atmosphere 

 destitute of oxygen for not longer than 20 hours, no loss of albumen 

 takes place. (2) If, however, the plants have been previously deprived 

 of their non-nitrogenous substance, they will, in these circumstances, lose 

 a portion of their albumen in the first 20 hours. (3) The decomposition 

 of albumen can maintain the life of a plant for a time in an atmosphere 

 containing no oxygen ; (4) this decomposition is independent of the 

 atmospheric oxygen ; (5) the decomposition of albumen which takes 

 place in a non-oxygenous atmosphere during the fourth and fifth days is 



* But. Ztg., xlvi. (1888) pp. 469-78, 485-92. t See this Journal, 1888, p. 259. 



X ' Stud. u. Exper. iib. d. Chera. Vorgang d. Assimilation,' Erlungen, 1888, 36 pp. 

 § Ber. Deutsch. Bot. GeselL, vi. (1888) pp. 205-12. 



