782 SUMMARY OF CUllRENT RESEARCHES RELATING TO 



appear to have no other source of nitrogen ; vvhile, on the other hand, 

 this is not the case with vetches, which may grow luxuriantly in a soil 

 containing no nitrogen. They must, therefore, obtain this element from 

 some other source, which appears to be the free nitrogen of the atmo- 

 sphere. They are not, however, able to obtain it directly from the air ; 

 this is effected by microbes, which carry on a symbiotic existence with, 

 several species of Leguminosse, usually stored up in special tubercles on 

 the root ; they are not able to make use, for this purpose; of the microbes 

 contained in the soil. 



Power of plants to absorb Nitrogen from the air.* — Herr B. Frank 

 replies to the statements of Hellriegel and Willfarth, and maintains his 

 previous assertion,f that all plants possess the power, under certain 

 circumstances, of assimilating directly the free nitrogen of the air. The 

 contrary results obtained by Hellriegel and Willfartb in the case of 

 plants belonging to any other order than the Leguminosse, he attributes 

 to the plants being in a weak or unhealthy condition, in which state 

 they are entirely dependent for their nutrition on previously formed 

 organic nitrogenous compounds. He points out that there is no single 

 direct observation to connect the " bacteroids " in the root-tubers of 

 Leguminosse with this supposed function, that the fact of their being 

 living organisms is subject to very considerable doubt, and that their 

 structure and mode of life are altogether different from those of 

 " mycorhiza," in which a symbiosis between the fungus and the 

 enveloped root has been satisfactorily demonstrated. 



Movements of Gases in Plants.j— Herr P. Kruticki finds the per- 

 meability of different plants for air to vary exceedingly, and to bear no 

 relationshij) to their permeability for water. In winter the air contained 

 in the branches contains less oxygen and more nitrogen, and a con- 

 siderably larger proportion of carbon dioxide than atmospheric air. At 

 the beginning of spring the proportion of oxygen increases, while that 

 of carbon dioxide decreases ; until, when the buds begin to open, the 

 composition of the contained air is nearly that of the surrounding 

 atmosphere. This indicates a decrease in the activity of the physio- 

 logical processes within the plant in the winter. 



Curvature of Growing Organs.§ — Pursuing his investigations on 

 this subject, and replying to the observations of TsToll,!] Herr J. VVortmann 

 sums up the main results as follows : — The three variables which deter- 

 mine the growth of a cell are turgor, extensibility of the cell-wall, and 

 the presence or access of water ; every alttiration in any one of these 

 forces brings about a change in the growth. As long as a cell grows, 

 the production of osmotic substances in the cell-sap and of elements of 

 the cell-wall, and absorption of water must continue. The increased 

 extensibility of the cell-wall of the under-side of a cell which is curving 

 upwards (epinastic) is the result of a diminished formation of cell-wall, 

 while the diminished extensibility of the cell-wall of the upper side is 

 the result of an increased formation of cell-wall. 



* Ber. Deutsch. Eot. Gesell., vii. (1889) pp. 234-47. 



t Cf. this Journal, ante, p. 550. 



X Script. Bot. Horti Uuiv. Imp. Pelropolitana3, ii. (1 888) pp. 115-53. See Bot. 

 Centralbl., xxxix. (1889) p. 30. 



§ Bot. Ztg., xlvii. (1889) pp. 453-61, 409-80, 485-92. Cf. this Journal, ante, 

 p. 02. II Cf. this Jonrn:il, ante, p. 413. 



