313 



i. Changes Due to a Lack of Oxygen. 



General Phenomena. 



It is to be assumed as well known that, with the cessation of the supply 

 of oxygen, the protoplasmic currents gradually come to a standstill (oxygen 

 rigor.) Kiihne^ observed that in an atmosphere of hydrogen the motion in 

 the stamen hairs of Tradescantia virginica stopped after 15 to 20 minutes. 

 Wortmann- found that the parts of plants in air free from oxygen respired 

 at first exactly as much carbon-dioxid as those with an unimpaired supply. 

 Later a difference made itself felt in favor of the latter plants. Like the 

 gradual cessation of the cytoplasmic currents, this gradual retrogression in 

 the amount of carbon-dioxid with the exclusion of oxygen (intramolecular 

 respiration) indicates that the oxygen stored in the plant body is consumed 

 at first. Death from suffocation, therefore, takes place slowly, especially 

 since the green plant with sufficient illumination still decomposes carbon- 

 dioxid and water and thus forms oxygen for some time. Bohm^ detected a 

 small amount of oxygen in the volume of gas evolved when he enclosed the 

 green leaves of land plants in an atmosphere of hydrogen with sufficient 

 illumination. 



Aside from the cases which have been observed already in the divisions 

 on "Loamy soils" and "Too deep planting of trees," we will consider a few 

 occurrences of bad aeration as a result of closing the lumina of the ducts 

 forming the main water system. Such stoppage is especially serious for the 

 sap wood*. With Bohm^ we may picture to ourselves the process of aera- 

 tion as follows : There is not only a difference in pressure between the 

 outer air and the diluted air inside the ducts, but also a difference in con- 

 stituents. The enclosed air will give up its oxygen in the respiratory pro- 

 cesses more rapidly and take up the carbon-dioxid produced. This is either 

 soaked up, by the filling of the ducts with water, and carried off in the rising 

 sap current, or, since it penetrates the moist walls rather easily, is given out 

 in a radial direction by diffusion. The new and necessary oxygen which hi 

 lesser amounts may also enter through the roots with the air rich in oxygen, 

 dissolved in the water, will, nevertheless, under normal conditions get into 

 the plant mainly through transverse conduction. It diffuses more easily 

 through moist walls than does the nitrogen of the air, because water absorbs 

 it more abundantly than it does nitrogen. Since now the oxygen within the 

 plant body is utilized most but is also most easily capable of moving from 

 part to part, there results a prevailing diffusion stream of oxygen from with- 

 out inwards in each horizontal plane of a trunk. 



1 Untersuchungen iiber das Protoplasma. 1864, p. 89 and p. 106. 

 - Wortmann, tJber die Beziehungen der intramolekularen zur normalen At- 

 mung. Inauguraldis.sertation, Wurzburg, 1879. 



3 Bohm, tJber die Respiration von Landpflanzen. Sitzungsber. d. Kais. Akad. d. 

 Wissensch. in Wien, Vol. 67 (1873). 



4 Elfving, tJber die Wasserleitung im Holze. Bot. Z. 1882, No. 42. 



5 Bohm, J., tJber die Zusammensetzung der in den Zellen und Gefafsen des 

 Holzes enthaltenen Luft. Landwirtsch. Versuchsstationen Vol. XXI, p. 373. 



