14 BOTANY. 
glass, noting the wateriness. Lay the specimen aside for half an 
hour or so, and then note its shrinkage by loss of water. 
(0) Mount a few plants of Pond Scum (Spirogyra) in a very little 
water, Examine under the high power of the microscope, and while 
doing this flow glycerine under the cover-glass. The glycerine im- 
-bibing water with great avidity withdraws the water of the cell-sap 
from the cells, causing them to collapse. 
(c) The presence of sugar may be demonstrated in many cases by 
taste alone, as in the stems of cane and Indian corn. 
(d@) Cane-sugar when abundant may be crystallized out (in small 
stellate crystals) from cell-sap by the use of strong alcohol or glyce- 
rine. 
(e) Make thin slices of the root of the sunflower or dahlia, and soak 
for some days in alcohol: the inulin will appear in the shape of 
sphere-crystals of greater or less size, according as the crystallization 
has been slower or more rapid. 
(f) The presence of acids in the cell-sap of many plants may be 
shown by placing a moist cut surface in contact with blue litmus- 
paper. The latter will be distinctly reddened. 
Notsr.—In the study of minute objects it is now the general cus-. 
tom to use metric measurements. The units used are the millimetre 
and the micromillimetre, the former for the larger measurements, the 
latter for the smaller. A millimetre equals .0894 of an inch, or 
nearly one twenty-fifth of an inch. 
For the measurement of objects requiring high powers of the 
microscope the micromillimetre is used. It is represented by the 
Greek letter “7, or by mmm. It is one thousandth of a millimetre, 
and equals .0000894 of an inch, or nearly one twenty. five-thousandth 
of aninch. A spore is thus said to measure 15 wu in diameter, 35 u 
in length, etc., or in the absence of the Greek letters we may record 
these measurements as 15 mmm. and 35 mmm. In reading the fore- 
going we may of course say 15 micromillimetres and 85 micromilli- 
metres, but more commonly the contraction micro is used, or even 
the name of the Greek letter: thus we may say 15 micros, or 15 mu. 
