B88 riNGuicuLA VULGAEIS. CIIAP. xvi 



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 arable 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 for 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. 

 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 f 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 



