COMPOSITION IN SUCCESSITE STAGES. 205 



in Germany, at the same time, but independently of each 

 other, resumed the subject, and to their labors the sub- 

 joined figures and conclusions are due. 



Here follows a statement of the Periods at which the 

 plants were taken for analysis. 



. 1 June 18, Arendt— Three lower leaves unfolded, two upper Btill closed. 

 iBt Period ^ ,1 ]^g_ Bretschnekler— Four to five leaves developed. 

 3d Period I "^"^^ ^' ^^^ tlays,) At.— Shortly before the plants were fully Leaded. 



) " 39, (10 days,) Br.— The plants were headed. 

 „, p., (July 10, (10 days,) At. — Immediately after hloom. 

 1 "8, (9 days,) Br.— Full bloom. 



4th Period t-"^"'^ ^^' ^^^ ^'^^^•'> At.— Beginning to ripen, 

 i " 38, (20 days,) Br.— " " 



5th Period l'^'^^^ ^'^' t^" "^"y^'' At.-Fully ripe. 

 (Aug. 6, (9 days,) Br.— " " 



It will be seen that the periods, though differing some- 

 what as to time, correspond almost perfectly in regard to 

 the development of the jjlants. It must be mentioned 

 that Arendt carefully selected luxuriant plants of equal 

 size, so as to analyze a uniform material, (see p. 210,) and 

 took no account of the yield of a given surface of soil. 

 Bretschneider, on the other hand, examined the entire 

 produce of a square rod. The former procedure is best 

 adapted to study the composition of the well-nourished 

 individual plant / the latter gives a truer view of the crop. 



The unlike character of the material as just indicated is 

 but one of the various causes which might render the two 

 series of observations discrepant. Thus, differences in 

 soil, weather, and seeding, would necessarily influence the 

 relative as well as the absolute development of the two 

 crops. The results are, notwithstanding, strikingly accord- 

 ant in many particulars. In all cases the roots were not 

 and could not be included in the investigation, as it is im- 

 possible to free them from adhering soil. 



The Total Weight of Crop per English acre, at the 



end of each period, was as follows : 



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