388 PINGUICULA VULGARIS. Cuar. XVL 
fluid; and it particularly deserves notice that this, as on the 
former 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 @ 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 for as 
long a time as the leaf was observed. 
(19) Six small particles of dry sturch 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. 
30 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 2 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 I am 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. 
From the foregoing experiments and observations we 
