Marcs, 1909.] 



269 



SCIENTIFIC AGRICULTURE. 



STUDIES ON GERMINATION AND 

 PLANT-GROWTH. 



Summary. 



Soil which has been heated without 

 drying to temperatures from 60° to 150° 

 behaves unfavourably towards the ger- 

 mination of seeds, the total seeds ger- 

 minating decreasing (in most cases), and 

 the time necessary for their germination 

 increasing, with the temperature of, 

 heating. The average results are suffi- 

 ciently regular to show that the alter- 

 ation in the soil must begin at temper- 

 atures as low as about 30.° 



Sterilised seeds behave in the same 

 way as unsterilised ones, except that 

 the time required for germination is uni- 

 formly longer. This is due to an alter- 

 ation in the seeds by the sterilising agent, 

 and not to the destruction of bacteria, 

 for sterilised seeds do not recover their 

 property of ready germination on being 

 re-inoculated. Various sterilising agents 

 were examined, but mercuric chloride 

 was the only one found to be satis- 

 factory and efficient. 



The retarding effect on germination 

 produced by heating the soil cannot be 

 explained by an alteration in the bacte- 

 rial condition of the soil, for the alter- 

 ation extends progressively at temper- 

 atures beyond that sufficient to destroy 

 all bacteria ; moreover, no similar results 

 are obtained with sand, even when this 

 has been thoroughly impregnated with 

 soil-bacteria to start with ; also, re- 

 inoculating previously sterlised seeds 

 has no effect on their germination ; and 

 many seeds, after sterilisation, will ger- 

 minate freely in a sterile medium. 



By heating the soil, an increase in its 

 soluble constituents occurs, especially in 

 the soluble organic and nitrogenous 

 matter, and the increase in either of 

 these has been found to be directly pro- 

 portional, within the limits of experi- 

 mental error, to the increase in the time 

 required for germination. The latter- 

 increase appears, therefore, to be due 

 to the formation of a nitrogenous com- 

 pound in the soil, which is inhibitory 

 towards germination. This compound 

 is sufficiently stable in solution for an 

 extract of heated soil to affect an un- 

 heated soil when it is added to this latter ; 

 it also does not seem to be destroyed 

 when the soil containing it is kept at a 

 low atmospheric temperature for some 

 months ; but at a higher temperature, 

 and in the presence of sufficient mois- 

 ture, it generally loses some of its inhi- 

 bitory properties, probably through 

 oxidation, 



The inhibitory substance is not of an 

 acid nature. 



Soils from different localities favour 

 the germination of seeds to different 

 extents, the extent varying (in the three 

 instances examined) directly with the 

 amount of soluble organic matter in the 

 soil ; but, on heating these soils to the 

 same temperatures, their action is 

 exactly reversed, the soil richer in solu- 

 ble organic matter forming, on heating, 

 a large proportion of inhibitory matter, 

 and becoming, therefore, less favour- 

 able to germination. 



The experiments do not settle defi- 

 nitely whether any of the inhibitory 

 substances is ever present in soils before 

 artificial heating, but it seems probable 

 that such is the case. 



The temperature of* heating at which 

 the inhibitory substance is formed in 

 greatest quantity is about 200*; it dimin- 

 ishes in amount as the temperature is 

 further raised, till it disappears entirely 

 at a low red heat, such burnt soil behav- 

 ing in nearly the same way towards ger- 

 mination as does unheated soil. 



The substance which is inhibitory as 

 regards germination need not neces- 

 sarily be so as regards plant growth, 

 or it may become destroyed before 

 growth becomes active. Its presence 

 results in an increase in the soluble 

 nitrogen in the soil, and this may be 

 the chief, if not the sole, reason of the 

 increase of growth of non-leguminous 

 plants in heated soil. Preliminary ex- 

 periments with apple-trees have led to 

 similar results, there being a large 

 increase in growth, in leaf-formation, 

 and in the percentage of nitrogen in the 

 leaves, when the trees were grown in 

 heated soil. The increase, also, was 

 greater as the temperature of heating 

 had been higher. 



The heated soils, however, behaved 

 towards the starting into growth of the 

 tree in the same way as they did 

 towards the germination of seeds, this 

 starting into growth having been con- 

 siderably delayed by the heating.— 

 Woburn Experimental Fruit Farm. 

 19th Report, 1908. 



NITROGEN AND NITRAGIN. 



By Alfred J. Ewart, d.sc, ph. d., 



F.L.S., 



Government Botanist and Professor of 

 Botany at the Melbourne University. 



The chemical element nitrogen takes 

 an essential part in the composition of 

 all plants and is especially abundant in 



