on the same leaf, were more sensitive than others; but why this should
be so, I do not know.
FIG. 9. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles
closely inflected, from immersion in a solution of phosphate of ammonia
(one part to 87,500 of water.)
Besides the differences just indicated between the leaves immersed in
water and in weak solutions of ammonia, the tentacles of the latter are
in most cases much more closely inflected. The appearance of a leaf
after immersion in a few drops of a solution of 1 grain of phosphate of
ammonia to 200 oz. of water (i.e. one part to 87,500) is here
reproduced: such energetic inflection is never caused by water alone.
With leaves in the weak solutions, the blade or lamina often becomes
inflected; and this is so rare a circumstance with leaves in water that
I have seen only two instances; and in both of these the inflection was
very feeble. Again, with leaves in the weak solutions, the inflection
of the tentacles and blade often goes on steadily, though slowly,
increasing during many hours; and [page 141] this again is so rare a
circumstance with leaves in water that I have seen only three instances
of any such increase after the first 8 to 12 hrs.; and in these three
instances the two outer rows of tentacles were not at all affected.
Hence there is sometimes a much greater difference between the leaves
in water and in the weak solutions, after from 8 hrs. to 24 hrs., than
there was within the first 3 hrs.; though as a general rule it is best
to trust to the difference observed within the shorter time.
With respect to the period of the re-expansion of the leaves, when left
immersed either in water or in the weak solutions, nothing could be
more variable. In both cases the exterior tentacles not rarely begin to
re-expand, after an interval of only from 6 to 8 hrs.; that is just
about the time when the short tentacles round the borders of the disc
become inflected. On the other hand, the tentacles sometimes remain
inflected for a whole day, or even two days; but as a general rule they
remain inflected for a longer period in very weak solutions than in
water. In solutions which are not extremely weak, they never re-expand
within nearly so short a period as six or eight hours. From these
statements it might be thought difficult to distinguish between the
effects of water and the weaker solutions; but in truth there is not
the slightest difficulty until excessively weak solutions are tried;
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