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1905] MCCALLUM—REGENERATION IN PLANTS III 
roots at the end of the week were killed, but the stem was still alive, 
though wilted, and the buds were developing; the cotyledons were 
much shrunken from loss of water which had been drawn out by the 
strong solution. The plants lived for several weeks, the young shoots 
slowly developing, and then died as the solution became stronger 
through evaporation. In the } solution the development of the buds 
was slow but normal. In all the others it was quite active. 
Experiment 20.—The nutrient salt solution mentioned was made 
up in concentrations which approximate the following: 7.5;, 33,5, #5), 
Pon oo Tos To's 20 Poy as’ gram-equivalent solution. These 
concentrations are only approximate, for probably ionization is not 
complete in any, certainly not in the stronger solutions, and also 
sufficient KOH was added to make them neutral. As it is only the 
relative strengths of solution that are required, it was not necessary 
to determine the actual osmotic pressure. One plant was used for 
each solution, and as before the roots were in the solution and the 
cotyledons and the rest of the plant in the air. Each plant was cut 
off a few centimeters above the cotyledons. In the three strongest 
solutions the plants were entirely killed, wilting very rapidly. In the 
Toy gram-equivalent solution, after two weeks the roots were still alive 
but very much twisted and contorted, and so far as could be seen no 
growth had occurred in them. The development of the buds was 
slow but complete. In the next solution below this the growth of the 
buds was considerably faster, and in all the others it was normal. 
Similar plants with their shoots and leaves intact were put in the 74% 
and +4"; solutions and in two days the leaves had wilted down. 
Experiment 21.—The last experiment was repeated by cutting off 
hot only the stem but also the cotyledons. The result was the same, 
hew shoots slowly forming while the water was being withdrawn. 
The result of these experiments shows (1) that the buds in the 
axils of the cotyledons will not develop under the influence of maxi- 
mum turgidity of the cells so long as the upper part is still function- 
ing, and (2) that if the stem be cut off the buds will develop against 
4 partial plasmolysis of the plant. With the shoot intact no change 
Se the water content will start the buds into activity, so that the 
stimulus to their development does not need to include any change 
in the water content of the cells. The factor that is constant in all 
the cases is the removal of the growing points above. 
