ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



993 



If the cells bo taken just before asphyxia, just when tbo protoplasm is 

 ceasing to move at all, it will bo found that tbey are no longer able to 

 assimilate. They are still quite normal, but if now placed in an illuminated 

 chamber, and supplied as before with carbonic acid, the rotation will not 

 return. A little free oxygen restores the original state, but without this, in 

 spite of the presence of light, chlorophyll, and carbonic dioxide, no oxygen 

 is formed. This state Pringsheim calls " inanition " or " Ernahrungs- 

 ohnmacht." "What has been noted in regard to its occurrence goes to show 

 the dependence of assimilation on the absorption of oxygen. 



But it is also a fact that the same phenomena of inanition occur when 

 cells in similar circumstances are kept continuously in the light. Eepeating 

 the above experiment with continuous illumination instead of darkness, 

 Pringsheim again observed the stoppage of rotation, and with it the cessation 

 of the liberation of oxygen. The absence of free oxygen is again the condition 

 of cessation of function ; if a small quantity be introduced the life revives, 

 if at least the inanition has not gone too far. 



How is this to be explained in terms of the generally accepted theory 

 of assimilation ? If the disruption of carbonic dioxide loitliin the cell furnishes 

 oxyrjen directhj, how should any assimilating cell suffer from want of oxygen ? 

 Pringsheim does not admit the usual assumption italicized above. His 

 opinion is that the analysis of the carbonic dioxide in assimilation does not 

 directly furnish oxygen, but that some other substance is formed, which, 

 passing diosmotically to the surface, breaks up and liberates free oxygen. 

 He criticizes the usual arguments based on the results of gas analysis. 

 What the substance is which forms oxygen at the surface ho is not yet 

 prepared to state. 



If this be so, the breaking up of carbonic dioxide and the liberation of 

 oxygen are two processes, distinct both in space and time, the one occurring 

 wdthin the cell, the other at its surface. This view is supported by reference 

 to the peculiar liberation of oxygen exhibited in darkness by both green and 

 unpigmented cells towards death. The bacterium-method proves this fact 

 iucontestably. This liberation of oxygen in darkness, and quite indepen- 

 dent of contemporaneous assimilation, may be termed " intramolecular 

 liberation of oxygen," and, according to Pringsheim, the normal liberation 

 is an essentially similar process, resulting from the disruption of an exos- 

 mosing substance. 



He advances other arguments to show that we are not warranted in con- 

 cluding, as has been hitherto done, that the presence of chlorophyll, light, 

 and carbonic dioxide exhaust the conditions of assimilation, and that in 

 estimating its amount no other factors but light-energy and the absorption of 

 light by the chlorophyll have to be taken into account. Assimilation is, on the 

 contrary, a physiological function of the protoplasm, and, like the movement, 

 depends on the presence of free oxygen. Physiologists will look with 

 interest for Pringsheim's detailed account of his investigations on this 

 important subject. 



Influence of Stretching on the growth of Plants.* — Dr. M. Scholtz 

 has experimented on the influence on the growth in length of various plants 

 — Helianthiis annuiis, Tropseolum majus, Fagopyrum esculentum, Linum usita- 

 tissimum, Ipomsea purpurea, Sinapis alba, Cucumis sativtis — of weighting the 

 growing stems with small weights, varying from 5 to 150 grammes. The 

 possibility of heliotropic curvatures was carefully excluded. 



He finds that the weight exercises on the growing stems two opposite 

 influences, the one accelerating, the other retarding the growth. Both take 



* Cohn's Beitr. z. Biol, der Pflanzen, v. (1887) pp. 323-64. 



