relative to the Motum of the Sap in Plants. 173 
the aid of his microscope. Amici has now discovered in it new 
laws of moti(:)n and new organs, which had escaped the observa- 
tions of Corti, and which throw new light on the physiology of 
plants in general, and particularly on the much contested po- 
rous tubes of Mirbel, and their functions in the economy of 
plants. Professor Amici’s experiments were made from the 
year 1814 to 1818 ; they were cai’efully noted in his journal, 
and are now fully and circumstantially described in the memoir 
to which we have alluded. The following is, in substance, the 
result of his observations. 
In all the parts of this plant, in the most delicate fibres of the 
root, as well as the finest green tendrils of the stem and branches, 
we may observe a regular circulation of the sap which they 
contain ; while transparent globules of various sizes are con- 
stantly and regularly moving in uninterrupted circulation, with 
a velocity gradually increasing from the centre towards the 
sides in two opposite alternating streams, up and down, in the 
two halves or sections of the same simple cylindrical canal or 
vessel (separated by no partition), which runs lengthwise through 
the fibres of the plant, but which is interrupted at certain inter- 
vals by knots, and closed up by a partition which limits the cy- 
clus. The circulation proceeds thus throughout the whole 
plant, and in all its fibres, from one knot to another ; and in 
every tract or portion limited, as above described, in itself, and 
totally independent of the rest. 
In general, the motion is perpendicular up and down; in 
some fibres, however, it is spiral, so that the ascending streams, 
which were seen at first on the right hand, appear next on the 
left, and vice versa. In the fibres of the root, the circulation is 
quite simple, as only one single central canal appears ; but in 
the green tendrils of the plant, the great central canal is sur- 
rounded by a number of similar small vessels, which have 
all a similar structure; but in each divided from it by ap- 
propriate partitions, so that they may be completely separated 
from it, each of them having a similar perpendicular or spiral 
circulation peculiar to itself. 
If one of these vessels be slightly tied, or bent in an acute 
angle, the circulation will be interrupted, as in the case of a na- 
tural knot, and will then proceed above and below the ligature 
or bend, as before, along the wliole tract. When restored to its 
