CHAP. XIII. 
CIRCULATION OF THE SAP. 
391 
nically compressed by it, or whether the duration of the cold 
causes contraction by a vital action, the roots commence 
causing a considerable discharge of fluid from the lower part 
of the apparatus. This goes on night and day, except when 
the pipes to carry off the sap are' frozen. As soon as a thaw 
comes on and the earth is relaxed, the roots, emptied of their 
juices, find themselves below their point of saturation ; they 
then emit nothing, but on the contrary absorb the descending 
juices. I satisfied myself of this not only by my apparatus, 
but in sawing through the trunk of a large poplar tree, a 
yard from the ground. The surface of the section of the 
stump was dry, but that of the trunk itself dripped with 
water.” 
The motion of the sap appears to be of two kinds; 1. ge- 
neral^ and 2. special : these must be carefully distinguished. 
The former is what has been alluded to in the preceding ob- 
servations ; the latter is altogether of a difierent nature, and 
exists in two entirely different conditions, generally con- 
founded with each other, till distinguished by Professor 
Schultz. Of these, the first is called Rotation, the latter 
Cyclosis ; the two are said never both to occur in the same 
species. 
Of Rotation. 
This kind of motion is confined to plants of a low organi- 
sation, but not entirely to flowerless or cellular families. It, 
however, forms for Professor Schultz an important physio- 
logical means of separating the vegetable kingdom into two 
primary classes, namely, Homorgana and Heterorgana : the 
former of which, consisting wholly or in great measure of 
cellular tissue, contains all the cellular flowerless, and some 
flowering plants of a low organisation; the latter all the 
higher flowering plants, and the vascular flowerless. It 
consists in a special circulation of the fluid contained in the 
interior of each cell, and is always so limited; the rotation in 
one cell never interposing or mixing with that in another cell. 
The rotating sap of such plants is said by Schultz to have 
the power of absorbing coloured fluids, while the cinenchy- 
matous vessels, in which cyclosis goes on, either do not take 
c c 4 
