1913] SHULL—SEMIPERMEABILITY OF SEED COATS 185 
gives the highest osmotic pressure of any known neutral salt, was 
employed. The imbibition curve for air-dry seeds known to 
contain 8-9 per cent of moisture is shown in fig. 6. In the case of 
both lower and upper seeds there was found a slight loss in weight 
during the first few hours of soaking in this concentrated LiCl 
solution. The loss is very small in amount, averaging 0.5 mg. per 
seed in all the tests made. But 
after the seeds have been in the 5 - 1 a 
solution for 6 or 7 hours, there is 
a very slow increase in weight, so 
that at the end of 46 hours the 
weight of the soaked seeds was the same as when first put into the 
fluid. The exact significance of this behavior is not very clear, but 
it is obvious that these seeds do not possess internal forces of 
sufficient magnitude to withdraw any water from 
2 the LiCl solution. 
In order to test the balance between osmotic 
pressure and the internal forces further, a number 
of seeds were soaked first in water until they had 
taken up about 44 per cent of their dry weight. 
They were then placed in saturated LiCl, which was 
kept saturated by keeping 40-50 grams of the undis- 
solved salt in the bottom of the vessel and stirring 
it up frequently. 
. The imbibition 
poiiiiiyiiiiity, curve is shown 
Fic. 7.—Curve showing loss of water from seeds soaked in fig. 7. At the 
in water before transferring to saturated LiCl solution; end of one hour, 
imbibition force of air-dry seeds and osmotic pressure of 
saturated LiCl solution approximately equal. 
Fic. 6.—Imbibition curve for air-dry 
seeds in saturated LiCl solution. 




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more than three- 
fourths of the 
water had been withdrawn, and in 7 hours the seeds were only 
2.5 per cent above their air-dry weight. The water was with- 
drawn more and more slowly until at the end of roo hours they 
reached their original dry weight. The results shown in figs. 6 and 7 
indicate that capillarity and imbibition force in an air-dry seed of 
Xanthium, that is, one with 8-9 per cent of moisture, is approxi- 
mately equal to the osmotic pressure of a saturated solution of LiCl. 
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