326 HOW CEOPS GROW. 



Oxygen Gas needM to Assimilation. — Traube has made 

 some experiments, which seem to prove conclusively that 

 the process of assimilation requires free oxygen to surround 

 and to be absorbed by the growing parts of the germ. 

 This observer found that newly-sprouted pea-seedUngs 

 continued to develope in a normal manner when the cot- 

 yledons, radicles, and lower part of the stem, were with- 

 drawn from the influence of oxygen by coating with var- 

 nish or oil. On the other hand, when the tip of the 

 ■plumule, for the length of about an inch, was coated with 

 oil thickened with chalk, or when by any means this part 

 of the plant was withdrawn from contact with free oxygen, 

 the seedling ceased to grow, withered, and shortly perish- 

 ed. Traube observed the elongation of the stem by the 

 following expedient. 



A young pea-plant was fastened by the cotyledons to a 

 rod, and the stem and rod were both graduated by deli- 

 cate cross-lines, laid on at equal intervals, by means of a 

 brush dipped in a mixture of oil and indigo. The growth 

 of the stem was now manifest by the widening of the 

 spaces between the lines ; and by comparison with those 

 on the rod, Traube remarked that no growth took place 

 at a distance of more than 10-12 lines from the base of 

 the teiminal bud. 



Here, then, is a coincidence which appears to demonstrate 

 that free oxygen must have access to a growing part. 

 The fact is further shown by varnishing one side of the 

 stem of a young pea. The varnished side ceases to extend, 

 the uncoated portion continues enlarging, which results in, 

 and is shown by, a curvature of the stem. 



Traube further indicates in what manner the elabora- 

 tion of cellulose from siigar may require the cooperation 

 of oxygen and evolution of carbonic acid, as expressed by 

 the subjoined equation. 



Glucose. Oxygen. Carbonic Add. Water. CeUxdose. 



3 (Cij Hj, 0,s) + SiO = 12 (CO2) + 14 (HjO) + Cj. Hj„ 0,o. 



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