92 
Effect of Tension on Plants. 
the usual thickenings of cell walls was found after a few days. This 
epitrophy is not counterbalanced by a later hypertrophy, at least, not 
during the time of observation, which was four weeks. 
Y. Again, plants were laid horizontal and at a distance of four or 
five inches from the base, sharply bent downwards over a glass rod, and 
held in this position by means of thread and weights for four or five 
weeks. Here also a great stress must have been at work upon the tissues 
of the curved portion, as well as gravitation. Hypertrophy occurred in 
the horizontal part on the upper side but not to any marked extent at the 
curve. Again the number of bast cells undergoing thickening was less 
than in the normal plant, the groups of thick walled cells being separated 
by rays of parenchymatous tissue. Figs. 4 and 5 show a cross section 
of a castor bean plant 28 days old, which was bent in the manner de- 
scribed for 21 days. Fig. 4 is the upper, 5 the lower side. Fig. 3 shows 
a normal of same age. 
At the point of curvature on the concave side a sharply defined line 
often appeared. This line stained with chlor-zinc-iodine exactly like 
wood fibres and apparently consisted of compressed disorganized rows 
of cells. Occasionally, small thick walled cells could be detected in it. 
In addition to this, active cell proliferation occurred just without and 
contiguous to the bast. These cells were very thin walled and strongly 
resembled those of the phellogen of bark. 
YI. \ Seedlings were laid horizontal and bent around a rod as before 
but this time in the horizon. Thus, gravitation acted upon the upper 
side while the outer flank of the stem was strongly stretched. Ho thicken- 
ing whatever occured. on the flank but the usual state of affairs was 
always found in the upper side. 
YII. Young bean plants were bent at a height of 3 to 4 inches at right 
angles, the upper part being confined to the horizontal position, again 
allowing both tension and gravitation to coincide in their action. Sec- 
tions made at intervals of % inch from the base to the leaflets showed 
that hypertrophy began at a distance of about *4 inch from the point 
of greatest curvature and increased in amount on and over the curve, 
reaching its highest development however in the horizontal part at some 
distance from the curve. At the point where both factors were at work 
the effect was not so great as where only one was active. A‘t the inner 
curve, as in the other cases, the cell walls of all tissues directly under 
the contact surface, were very poorly developed and resembled paren- 
chyma cells, the tissues being thrown into calluslike ridges and folds. 
YIII. Well advanced seedlings of Phaseolus and Ricinus were now 
inversely placed and then bent in to the horizon and secured. After 
geotropic action was well advanced, the whole plant presents a figure 
like the three sides of a rectangle, of which the angle, or rather curve, 
