50 
REPORT ON BOTANY, MDCCCXLI : 
belongs as little to the usual course of vegetation, as the 
human uterus can be said to be a blood vessel on account of 
its menstruating. A considerable quantity of fluid flows out 
rapidly from the cut stem of the Hoya carnosa in our hot- 
houses, but the microscope instantly shows, that all the spiral 
and porous vessels carry only air.” 
The answer derived from the rapidity of the flowing out of 
sap is not worth much ; for every Botanist knows, or may 
readily convince himself, by placing a slice of a potato 
under the microscope, and adding a drop of tincture of iodine, 
when it progresses as rapidly through the walls of the cell as 
on the table, therefore the living membrane of the cell offers 
little or no resistance to the absorption of fluids. In the 
same way as inorganic substances are permeable (most of the 
perfect crystals, at least of the alkalies and earths) to the 
imponderables, light, warmth, &c., so also is the organic 
substance permeable for fluids. It is not the passing through 
of a fluid, which is the effect of a vital power, which requires 
explanation, but quite the reverse ; it is the retention of the 
fluids in certain cells, which either originates from a parti- 
cular organization, as in the epidermis, or from the difference 
of the medium on both surfaces (air and fluid), as, for 
instance, in the air cells, or from peculiar organic powers, as, 
for instance, in the cells with coloured juices, existing between 
the cells with uncoloured juices. 
Since the lifeless vegetable membrane retains fluids, the 
most simple method is to attribute this as a primary quality 
also to the living membranes, and to search only for par- 
ticular powers when they allow a fluid to pass through them. 
The juice which flows from the Hoya carnosa^ comes from 
the proper vessels, sap vessels, the same as the milky juice in 
the Asclepiadaoece. These vessels generally, however, have 
no partitions. If, then, the nutritive sap made a rapid tran- 
sition from the spiral vessels into the cells (withered twigs, 
for instance, placed in water, very quickly erect their leaves), 
would it be seen? But this is not the place for the 
investigation of this subject; it was only necessary to give 
Br, Schleiden’s statement in his own words, 
442 
