SP Sa ee Re oe ne aa ee a ons. ea ees ee 
gto] PENNINGTON—LONGITUDINAL COMPRESSION 261 
of bending read in degrees upon the arc of the protractor mn. 
The testing weight for each series of plants was selected so that the 
plants would not be broken or too strongly bent. The pulley p 
could be adjusted as indicated by dotted lines, in order that the 
weight should at all times act in the direction perpendicular to the 
stem. This method was found to show very slight differences in 
the rigidity of stems. 
The resistance to crushing was determined by the apparatus 
shown in fig. 2. A piece of the stem 10-15 mm. in length was 
placed with one end against the fixed block f, and the movable 
block m brought against the opposite end. The movable block was 
attached to the strong spring balance s, which in turn was attached 
b 
Fic. .2 
to the threaded rod ry. When the tail nut 6 was turned upon the 
rod r, the movable block m was drawn toward the fixed block f, 
_ thus subjecting the stem st to pressure. The amount of pressure 
could be read at once upon the scale of the balance. The resistance 
to crushing could be determined very sharply, for when the critical 
point was reached, the stem always gave way suddenly. 
After testing a piece for resistance to crushing, the part of the 
stem next to that which was crushed was put into alcohol to be pre- 
served for a study of the internal structure and microscopic meas- 
urements of the mechanical tissues. 
ANATOMICAL STUDY 
The anatomical studies and ts were made from cross- 
sections, which were suitably prepared and stained so as to differ- 
entiate more. clearly the various tissues, principally the xylem 
and hard bast, Chemical reactions (aniline sulfate with sulfuric 
acid, and phloroglucin with hydrochloric acid) as well as stains 
(acid fuchsin, aniline safranin, and methyl blue) were used. 
ol 
