Cnar. XVI.] SECRETION, ABSORPTION, DIGESTION. 313 
(17) A particle of white sugar, placed on a leaf, formed in 1 hr.10 m. 
a large drop of fluid, which in the course of 2 additional hours ran 
down into the naturally inflected margin. This fluid was not in the 
least acid, and began to dry up, or more probably was absorbed, 
in 5 hrs. 30m. The experiment was repeated; particles being placed 
on a leaf, and others of the same size on a slip of glass in a moistened 
state; both being covered by a bell-vlass. This was done to see 
whether the increased amount of fluid on the leaves could be due to 
mere deliquescence; but this was proved not to be the case. The 
particle on the leaf caused so much secretion that in the course of 4 hrs. 
it ran down across two-thirds of the leaf. After 8 hrs. the leaf, which 
was concave, was actually filled with very viscid fluid; and it particu- 
larly deserves notice that this, as on the furmer occasion, was not in the 
least acid. ‘This great amount of secretion may be attributed to exosmose. 
The glands which had been covered for 24 hrs, by this fluid did not 
differ, when examined under the microscope, from others on the same leaf, 
which had not come into contact with it. This is an interesting fact in 
contrast with the invariably aggregated condition of glands which have 
been bathed by the secretion, when holding animal matter in solution. 
(18) Two particles of gum arabic were placed on a leaf, and they 
certainly caused in 1 hr. 20 m. a slight increase of secretion. This 
continued to increase for the next 5 hrs., that is fur as long a time as 
the leaf was observed. 
(19) Six small particles of dry starch of commerce were placed on a 
leaf, and one of these caused some secretion in 1 hr. 15 m., and the 
others in from 8 hrs. to 9 hrs. The glands which had thus been 
excited to secrete soon became dry, and did not begin to secrete again 
until the sixth day. A larger bit of starch was then placed on a leaf, 
and no secretion was excited in 5 hrs, 80 m.; but after 8 hrs. there 
was a considerable supply, which increased so much in 24 hrs. as to 
run down the leaf to the distance of-? of an inch. This secretion, 
though so abundant, was not in the least acid. As it was so copiously 
excited, and as seeds not rarely adhere to the leaves of naturally 
growing plants, it occurred to me that the glands might perhaps have 
the power of secreting a ferment, like ptyaline, capable of dissolving 
starch; so I carefully observed the above six small particles during 
several days, but they did not seem in the least reduced in bulk. A 
particle was also left for two days in a little pool of secretion, which 
had run down from a piece of spinach leaf; but although the particle 
was so minute no diminution was perceptible. We may therefore 
conclude that the secretion cannot dissolve starch. ‘The increase caused 
by this substance may, I presume, be attributed to exosmose. But 
Iam surprised that starch acted so quickly and powerfully as it did, 
though in a less degree than sugar. Colloids are known to possess some 
slight power of dialysis; and on placing the leaves of a Primula in 
water, and others in syrup and diffused starch, those in the starch 
became flaccid, but to a less degree and at a much slower rate than the 
leaves in the syrup ; those in water remaining all the time crisp. 
