GBRMIKATION. 365 



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 means this part of the plant was withdrawn from contact 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 perished. 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 naixture 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 ten to twelve lines from 

 the base of the terminal bud. 



Here, then, is a coincidence which appears to demon- 

 strate 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 a cti^jyature of the stem. 



Traube further indicates in what manner tlie elabora- 

 tion of cellulose from sugar may require the co-operation 

 of oxygen and evolution of carbon dioxide, as expressed 

 by the subjoined equation. 



Glucose. Oxygen. Carbon dioxide. Water. Cellulose. 



2(C,jH„0ij) -1-24 = 12 (CO,) -I- 14(H,0) -|- C„Hj,Ou,. 



When the act of germination is finished, which occurs 

 as soon as the cotyledons and endosperm are exhausted 

 of all their soluble matters, the plant begins a fully inde- 

 pendent life. Previously, however, to being thus thrown 

 upon its own resources, it has developed all the organs 

 needful to collect its food from without ; it has unfolded 

 its perfect leaves into the atmosphere, and peiTaded a 

 portion of soil with its rootlets. 



