1896] MOVEMENT AND TRANSMISSION OF IMPULSES IN PLANTS 295 
for the construction of a machine which shall react similarly to 
Mimosa. 
All pulvinar movements are supposed to be due to a loss of 
water from the portion of the pulvinus in which contraction 
ensues, either directly by transpiration, or by withdrawal by 
the action of neighboring tissue so affected. : 
Scant attention is paid to the results of Pfeffer and his 
students, but the author gives the records of a very large 
number of experiments which, as he rightly points out, show 
reactions quite different from those obtained in northern 
latitudes. The thermometric records are meager in certain 
series, but it is possible that the temperature variations do not 
exert such an important influence in the tropical habitat of the 
plant. » 
According to Haberlandt3 and others, the transmission of 
impulses and reaction in Mimosa bears a direct relation to the con- 
ditions securing an excessive root supply of water and hindered 
transpiration, Cunningham, however, finds the relation an inverse 
one, that plants in a saturated atmosphere react least readily. 
Ina comparison of the three most important forms of stimuli he 
Says: “In cases of ‘contact stimulation’ we induce mere local 
distributions of liquid within the tissues ; in cases of incision we 
Sive rise to temporary exudations from the general supply of 
liquid ; in cases of heating we secure not only this, but in addi- 
tion we establish temporary increase of transpiratory loss and a 
Site of persistent abnormal drain.” In what manner a contact 
stimulus may cause alterations in the transpiration of acell with- 
Out the interposition of protoplasmic action is not explained. It 
must be said, however, that Dr. Cunningham's observational 
results are of great value, and are very suggestive as to methods 
useful in a continuance of the work. 
ADDITIONAL EXPERIMENTS. 
at During the summer of 1895 I was enabled to make a number 
“xperiments with a view of-determining the chief factors 
3 H * 
Reizleitende Gewebesystem der Sinnpflanze. 1890. 
