390 HooKER: MOVEMENT IN DROSERA ROTUNDIFOLIA 
centration of osmotically active material dissolved in their cells 
was measured by plasmolysis. For this purpose solutions of 
potassium nitrate and glucose were prepared. The osmotic con- 
centration of plant cells may be compared with the concentrations 
of these substances in terms of their relative osmotic values. 
Consequently osmotic concentrations will. be measured in atmos- 
pheres as follows: 
Solutions of KNO; Solutions of glucose 
Atmospheres in percentages in percentages 
iS SENDA rs) SE rere ae gee eer t Oe aM bare a ea ae 3-8 
OG cede ne taep ee ecke Se sok ais ee ees 4.62 
oy ME Seer art Serato haters dma Soe Se ZOO pik eas OE eRES 5-40 
CS Ea A TET Se TAT Ee Ne aha ak Da hed 2 oe eee 6.17 
[PRO Re prs Oey a ar MSF ce OE es agi 6.905 
EDEL Aaa Rican wOee On ee DBO uaa Wipe. by Se eas oa 
EL nine Care ei x va 3, Dame Gta oeas eu 7 Pees oa 8.48 
Rea wate as Wee eis SAS cn SE oe as Oe 9.25 
ES Wie cee ek koe ee a = Oy & ab ard Paey pg eer e are ae 10.02 
ES Bei Ae i eee BOOS Ee cE NSS Oes aS 10.80 
4 aeRO ap Fer areeee peer te ges pe ye Ts Pananera  eetneTr eee. ee 11.58 
Tentacles of the Drosera were removed from the leaf with 
forceps, placed in prepared solutions, mounted and examined under 
the high power of the microscope. Plasmolysis was found to be 
most readily detected in slightly pigmented cells, and whenever 
possible tentacles with stalks composed of such cells were selected. 
In case aggregation occurred, the first traces .of plasmolysis were 
much more difficult to make out. Tentacles were treated and 
examined when straight; just after bending in response to a tactile 
stimulus; when fully bent; during unbending; and when again 
straight. The first procedure was to place tentacles in each of the 
prepared potassium nitrate solutions and to examine them for 
traces of plasmolysis. The results obtained by this general 
orientation were repeated and verified by numerous subsequent 
experiments both with potassium nitrate and with glucose solu- 
tions. The data given with glucose solutions were practically 
identical throughout with the results furnished by the potassium 
nitrate solutions. The final data given below are expressed in 
terms of the most concentrated solution that failed to plasmolyze. 
The epidermal cells on the pedicels of the tentacles have 
strongly cutinized outer walls which are impermeable to salt and 
sugar solutions. The solution reaches the inner cells of the ten- 
