DEVELOPMENT. 81 



maturation then consists in the gradual cessation of the 

 work done in the leaf, the exhaustion of its supplies car- 

 bonaceous, nitrogenous, and mineral and the transport of 

 these materials to the organs of reserve, to the bark and 

 young wood of the tree, to the seed in the case of wheat 

 and other annuals, to the roots, bulbs, and tubers in other 

 cases. In the case of an annual herbaceous plant like the 

 wheat it appears that both root-act on and leaf-action be- 

 come reduced to a minimum, or are even altogether stopped 

 some two or three weeks before the wheat is ready to cut, 

 so that during that period no increase of weight of the 

 plant as a whole takes place ; and if the ears themselves 

 increase in weight, it is because they derive matter from 

 other parts of the plant, which diminish in weight in pro- 

 portion. A few figures cited by M. Deherain will illustrate 

 the truth of these remarks thus in the case of colza, out 

 of a total of 1000 parts (grammes) of phosphoric acid in 

 the entire plant, 456 were found in the leaves in March, 

 and only 25 in the leaves in June, while the flowering 

 stems at the latter period contained 860. Results of a 

 similar character might be quoted in the case of potash 

 and albuminoid matters. In all cases while the relative 

 proportions gradually decline in the leaves they become 

 correspondingly augmented in the flowering part of the 

 stem and in the seeds. 



These results are attributed by M. Deherain in great 

 degree to varying degrees of evaporating power possessed 

 by the leaves. According to him, the older leaves at the 

 base of the stem evaporate but little as compared to the 

 younger leaves near the top. These, by their superior 

 evaporating power, cause the lower parts to be emptied of 

 their contents, which are thus forced upwards towards the 



