CHAP. I. ACTION OF THE PAETS. 13 



well as the blade remain inflected over an object placed 

 on the disc, depends on various circumstances ; namely 

 on the vigour and age of the leaf, and, according to 

 Dr. Nitschke, on the temperature, for during cold 

 weather when the leaves are inactive, they re-expand 

 at an earlier period than when the weather is warm. 

 But the nature of the object is by far the most 

 important circumstance ; I have repeatedly found that 

 the tentacles remain clasped for a much longer average 

 time over objects which yield soluble nitrogenous 

 matter than over those, whether organic or inorganic, 

 which yield no such matter. After a period varying 

 from one to seven days, the tentacles and blade re- 

 expand, and are then ready to act again. I have seen 

 the same leaf inflected three successive times over 

 insects placed on the disc ; and it would probably 

 have acted a greater number of times. 



The secretion from the glands is extremely viscid, 

 so that it can be drawn out into long threads. It 

 appears colourless, but stains little balls of paper pale 

 pink. An object of any kind placed on a gland always 

 causes it, as I believe, to secrete more freely ; but 

 the mere presence of the object renders this difficult 

 to ascertain. In some cases, however, the effect was 

 strongly marked, as when particles of sugar were 

 added ; but the result in this case is probably due 

 merely to exosmose. Particles of carbonate and phos- 

 phate of ammonia and of some other salts, for instance 

 sulphate of zinc, likewise increase the secretion. Im- 

 mersion in a solution of one part of chloride of gold, 

 or of some other salts, to 437 of water, excites the 

 glands to largely increased secretion; on the other 

 hand, tartrate of antimony produces no such effect. 

 Immersion in many acids (of the strength of one part 

 to 437 of water) likewise causes a wonderful amount of 



