DEVELOPMENT. 79 



gration of these elements has been well studied in the 

 case of the wheat by M. Isidore Pierre, who has conclu- 

 sively shown that what the leaves lose in these respects 

 is gained by the ear. One important feature of matura- 

 tion then consists in the gradual cessation of the work 

 done in the leaf, the exhaustion of its supplies carbo- 

 naceous, 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-action and leaf- 

 action become 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 in- 

 crease 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 proportion. A few figures cited 

 by M. Deherain Avill illustrate the truth of these remarks 

 thus in the case of colza, out of a total of one thousand 

 parts (grammes) of phosphoric acid in the entire plant, 

 four hundred and fifty-six were found in the leaves in 

 March, and only twenty-five in the leaves in June, while 

 the flowering stems at the latter period contained eight 

 hundred and sixty. Results of a similar character might 

 be quoted in the case of potash and albuminoid matters. 

 In all cases while the relative proportions gradually de- 

 cline in the leaves they become correspondingly augment- 

 ed 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 



