ABSORPTION AND TRANSMISSION OF FLUIDS BY CELLS, 781 — 
here that great light retards growth, as shown by the compara- 
tive height attained by the Wild Hyacinth according to whether 
it grows at the edge of, or in the thick part of a wood. Moisture 
and warmth, on the other hand, encourage growth ; hence, if a 
greenhouse is allowed to be warmer at night than in the daylight, 
the plants therein contained become drawn up (leggy, as it is 
termed) and weak. 
For the purpose of measuring accurately the rapidity of 
growth, some such instrument as that shown in jig. 1138, and 
called an Auxanometer, is employed, where at the end of the 
Jong arm of a lever a, is a pen b, which marks on a revolving 
drum c, covered with smoked paper. To the hook on the short 
arm of the lever a, is attached the one end of a thread, the other 
end being fastened to the tip of the stem. As the stem grows, 
the long arm of the lever, which is weighted, falls, and a record 
traced on the drum c, which may travel continuously, or, as in 
Vines’ Auxanometer, make a movement only at certain intervals 
of time, which are regulated by the clockwork arrangemen? at d. 
(2) Absorption and Transmission of Fluids.—The cell-wall of 
all young and vitally active parenchymatous or prosenchymatous 
cells is capable of readily imbibing : 
fluids, and we find, accordingly, that Fie. 1139. 
liquid matters are constantly being ab- cai 
sorbed and transmitted through such 
cells. The power which thus enables 
cells to absorb and transmit fluids is 
called osmose. This physical force, as 
will be afterwards shown, is a most im- 
portant agent in plant-life, for by its 
agency plants are enabled, not only to 
absorb crude food by their roots in a 
fluid state, but also to transfer it up- 
wards, from cell to cell, to the leaves 
and other external organs, for the pur- 
pose of being elaborated by the action of 
light, heat, and air. It is, moreover, by 
a somewhat analogous process (diffusion 
of gases) that the cells on or near the sur- 
face of plants are enabled to absorb 
and transmit gaseous matters. 
Osmose may be explained as follows: 
—Whenever two fluids of different densi- “ig. 1139. Apparatus to show 
= osmotic action. It consists 
ties are separated by a permeable mem- 6 4 bladder filled with 
brane which is capable of imbibing them, syrup, to the open end of 
there is always a tendency to. equalisa- SH tube & attached 
tion of density between the two, from _ yessel containing water. 
the formation of a current in both direc- 
tions, which will be modified by the action of the membrane, 
as well as by their own rates of diffusion. This osmotic action may 
