210 



phosphoric acid in the soil thus treated. Plants Avere gro\m in cylin- 

 drical pots (Wagner's) containing samples of the soils to be studied. 

 The effect of x>h<tsi)hatic fertilizers, as measured by the increase of yield 

 when they were applied, was compared with the amounts of plios])horic 

 acid extracted by acetic;, tartaric, oxalic, and citric acids and their salts. 

 From several hundred experiments which have been conducted during 

 2 years with some sixteen typical soils, it a]>i>('ars that a 1 per cent 

 solntion of citric acid generally serves to indicate the amount of phos- 

 ]>liori(' acid available to plants. There are, however, exceptions which 

 are not yet explained. In the <(nirse of the discussion of the paper, 

 Professor Orth of Berlin, whose stn«lies of soils are well known, 

 remarked upon the need of detaile<l study of the physical an«l geol«)gical 

 characters of the soil, and of the physiological habits of the plants 

 as well. It was exi»laiiied both by Dr. (ierlacli and by Prot»'ssor 

 Maercker that the results thus far obtained are regard«*d as tenta- 

 tive, and no final c«»nclnsions are yet made. They hope, however, by 

 their studies, which embrace not onl\ tlic geologit-al. physical, and 

 chenn'cal characters of the soils, bnt also tlu-ir agiicnltmai characters 

 as shown by i)ast and present «'xperience and cx|»erinicnt. lo work out 

 a reliable method for snch soil analysis as they are now attem])ting. 

 They contemitlate extending the in(|Miiy t<» other soil elements of ])lant 

 food, as jtotash and nitrogen. Inci(lentall_\ Professor Ma<'rcker stated 

 that the Wagner method of ]>ot cnlture had ]U'0ven very satisfactory. 

 Parallel experiments had Ix-en made in ordinary earthen pots with 

 results which agreed in the main with those obtained in the Wagner 

 cylind<'is. 



Another line of stndy with reference to the needs of soils and the 

 feeding capacities of jdants, namely, the growing of plants Mith ditler- 

 eut fertilizers and analyzing the ])roduce. was ])resented in a paper 

 by Professor Liebscher of the Agricultural Institute of tlie University 

 of Gottingen. This gave the results of a series of experiments which 

 have been in (quMation for se\«'ral years in the ex]teriniental garden of 

 the institnte. Ditferent plats of land were ti<'ated with nitrogen, ph()s- 

 phoric acid, and jtotash comjHMiiids. singly, two ]»y two, and all three 

 together. In the crops which grew u\)(iu them the ipiantities of the same 

 elements were determined. .Mthongh the resnlts thns tar (tbtained do 

 not warrant broad generalizations. Professor Liebscher hoi>cd tliat such 

 would be obtainal)le by further lu-osecution of the iiKpiiry. 



Professor Hellriegel addressed the meeting uiK»n quantitative vege- 

 tation experiments and individual factors of growth. He laid special 

 stress upon the imixutance of having the conditions of experiment 

 under control, and so regulating them that while the i)articular factor 

 in cpu'stion shonld be ada])ted to the inirimse of the «>xi>eriment, all the 

 others should be favorable. In this way and in this way alone can 

 exact studies of the effects of individual factors be made. He dwelt 



