40 BULLETIN OF THE BUSSEY INSTITUTION. 
Certain experiments of Hellriegel, on the composition of sap that was 
pressed out from clover plants of various ages, are not without interest 
in this connection, inasmuch as they indicate, in still another way, the 
fact that continuous washing is necessary in order to remove all the solu- 
ble matters of a plant. It was found, for example, that the expressed 
sap of young clover plants held in solution a much larger proportion of 
several of the ash ingredients, than the sap from old plants. Thus in the 
sap from young plants, there was found fully three-quarters of all the 
potash, that the entire plant contained, two-thirds of all the lime, half 
the chlorine, and not quite half of the magnesia; while of phosphoric and 
silicic acids, only about one-quarter of the whole amount was found in 
the expressed sap. In older plants, of the second year’s growth, Hellrie- 
gel got from the sap more than half of all the iime that was contained 
in the plants, and often as much as two-thirds of it; but he rarely found 
in the sap of these older plants as much as half of the entire potash, and, 
on the average of several experiments, he got only about one-third of 
that substance. So, too, a smaller proportion of the phosphorie acid and 
the silica was usually found in the sap of the older plants, while of mag- 
nesia he found in such sap some 80 or 90% of all that the plants con- 
tained. Almost the whole of the chlorine, also, was found in the sap of 
the old plants. Hellriegel satisfied himself by special experiments, upon 
thoroughly leached clover plants, that this retention of potash, in par- 
ticular, by the expressed stem and leaves of the older plants is not due, 
or at the least not to any great extent, to the deposition of insoluble com- 
pounds of potash within the plant. He inclines rather to the belief that 
certain kinds of cells, in particular parts of the plant, have become so 
firm and tough through age, that they resist the crushing action of the 
press, and retain the sap that was within them, as well as the potash, or 
what not, that the sap holds dissolves, while in the young plant all kinds 
of cells break readily, on being subjected to pressure, and give up their 
liquid contents. In this sense, Hellriegel supposed that the sap obtained 
from the older clover plants may have come, for the most part, from the 
softer parts of the tissue, and that it was not a fair sample of all that 
was actually contained in the plant. Difficulties analogous to this would, 
of course, be encountered in leaching any vegetable fibre, though they 
could be more fully overcome by the process of leaching than by that of 
mere pressing, because of the power of repeating the application of a 
‘solvent as often as may seem fit. 
In his well-known research upon the growth of the oat-plant, Arendt * 
endeavored to extract the whole of the soluble matters from the pul- 
verized, dry, ripe plants, by percolating the fine powder systematically 
with water. He found it impossible to obtain any useful results by ex- 
perimenting in this way upon the grain, but from the leaves and stems 
he dissolved out very considerable quantities of the ash ingredients. He 
* “Das Wachsthum der Haferpflanze,” Leipzig, 1859, pp. 166-187. 
