ANALYSIS OF THE VEGETATION OF THE GRAMINEjE. 589 



to become yellow and to wither completely. This effect first takes place 

 in the lowest leaves, and in each commences at the apex of the leaf and 

 gradually extends to the jjoint of insertion. When the leaves are com- 

 pletely withered, if they are gathered and submitted separately to the 

 tests that have been described, nothing can be found but some insensible 

 or nearly insensible traces of the saccharine principles and of the precipi- 

 table substance with which they previously abounded. Whence it appears 

 that at the period of which we are treating these carbonated principles 

 pass into the stem and serve it as an aliment, in the same manner as the 

 analogous principles, elaborated by the leaves of exogenous trees, de- 

 scend beneath the living cortical layer into the first external layers of 

 the alburnum, in order to nourish the young cylinder of wood and 

 bark, which like a hollow stem is annually formed and moulded upon 

 the ancient skeleton of wood. 



In rye and wheat the basis of the stems therefore derive nourishment 

 partly from the leaves which are attached to them and partly from the 

 soil. The summit of the stem may also be sujjplied with aliment by its 

 own leaves, and may raise the inferior sap ; but the ear, when it has left 

 the stem, and especially when it has been fecundated, appears to exercise 

 a powerful faculty of absorption upon the juices contained in the sum- 

 mit, which must remove them rapidly, in proportion as they are fur- 

 nished by the base of the stem. To satisfy myself that this was the 

 fact I divided the stems of wheat, from which the leaves had been re- 

 moved on the 4th of June, into two parts, the ear being in full flower. 

 Of the two extracts thus formed, that of the bases contained nearly 

 twice the quantity of sugar contained in the extract of the summits, 

 the densities being equal. At this period also of full eflflorescence the 

 saccharine principles are abundant in the ears of M'heat. They ex- 

 ist in them in the state of sugar of starch and cane sugar, adjoined to a 

 substance precipitable by alcohol, which is perfectly soluble in water, 

 and has a rotation to the right like dextrine, but having less rotating 

 energy and susceptible of modification by fermentation. The presence 

 of cane sugar in the ears is ascertained by the rotation of the extract, 

 which though strongly directed towards the right before fermentation, 

 is suddenly thrown towards the left, and becomes very feeble as soon 

 as that phaenomenon is completed. There was nothing to indicate 

 the existence of this sugar in the ears of rye before flowering, nor 

 in the young grains of rye, though the stems also contained cane sugar. 

 Could it arise from a difference of quality proper to the two plants ? 

 Whatever it might be they each present this remarkable result, that 

 the grape sugar of the stems does not pass in that state to the ears. 



As has been remarked above, in proportion as the fecundated ear is 

 enlarged the lower leaves become yellow and withered by transmitting 

 their carbonated products to the stem. The base of the stem also 



