ROOTS 5S 
Put some living threads of pond-scum (Spirogyra) (Chapter XX) 
into a4 per cent solution of glycerine in water, a 16 per cent solution 
of cane sugar, or (for quick results) a 2 per cent solution of common 
salt.1 Any one of these solutions is much denser than the cell-sap 
inside the cells of the pond-scum, and therefore the watery part of 
the cell-contents will be drawn out of the interior of the cell and 
the protoplasmic lining will collapse, receding from the cell-wall. 
The cell-contents are then said to be plasmolyzed. Sketch several 
cells in this condition. Remove the filaments of Spirogyra and 
place them in fresh water. How do they now behave? Explain. 
Repeat the plasmolyzing operation with another set of cells which 
have first been killed by soaking them for five minutes in a mixture 
of equal quantities of acetic acid, three parts to 1000 of water, and 
chromic acid, seven parts to 1000 of water. The pond-scum threads 
before being transferred from the killing solution into the plas- 
molyzing solution should be rinsed with a little clear water. Note 
how the cells now behave. How is it shown that they have lost 
their power of causing a liquid to be transferred mainly or wholly 
in one direction? Why do frozen or boiled slices of a red beet 
color water in which they are placed, while fresh slices do not? 
65. Osmosis in Root-Hairs. — The soil-water (practically 
identical with ordinary spring or well water) is separated 
from the more or less sugary or mucilaginous sap inside 
of the root-hairs only by their delicate cell-walls, lined 
with a thin layer of protoplasm. This soil-water will pass 
rapidly into the plant, while very little of the sap will 
come out. The selective action, which causes the flow of 
liquid through the root-hairs to be almost wholly inward, 
is due to the living layer of protoplasm (Chapter XII), 
which covers the inner surface of the cell-wall of the root- 
hair. When the student has learned how active a sub- 
stance protoplasm often shows itself to be, he will not be 
astonished to find it behaving almost as though it were 
1 This should be done as a demonstration by the teacher. 
