CuAP. III.] THE PROCESS OF AGGREGATION. 89 



glands, not only from its action being so rapid, but from' its effect 

 being somewhat different from tl;at of oilier salts. As the glands, 

 when excited, secrete an acid belonging to the acetic series, the 

 carbonate is probably at once converted into a salt of this series; 

 and we shall presently see that the acetate of ammonia causes 

 aggregation almost or quite as energetically as does the carbonate. 

 Ii a few drops of a solution of one part of the carbonate to 437 

 of water (or 1 gr. to 1 oz.) be added to the purple fluid which 

 exudes from crushed tentacles, or to paper stained by being rubbed 

 by them, the fluid and the paper are changed into a pale dirty 

 green. Nevertheless, some purple colour could still be detected 

 after 1 hr. 30 m. within the glands of a leaf left in a solution of 

 twice the above strength (viz. 2 grs. to 1 oz.) ; and after 24 hi"8. 

 the cells of the pedicels close beneath the glands still contained 

 spheres of protoplasm of a fine purple tint. These facts show that 

 the ammonia had not entered as a carbonate, for otherwise the 

 colour would have been discharged. I have, however, sometimes 

 observed, especially with the long-headed tentacles on the margins 

 of veiy pale leaves immersed in a solution, that the glands as well 

 as the upper cells of the pedicels were discoloured; and in these 

 cases I presume that the unchanged carbonate had been absorbed. 

 The appearance above described, of the aggregating process being 

 arrested for a short time at each transverse partition, impresses the 

 mind with the idea of matter passing downwards from cell to cell. 

 But as the cells one beneath the other undergo aggregation when 

 inorganic and insoluble particles are placed on the glands, the 

 process must be, at least in these cases, one of molecular change, 

 transmitted from the glands, independently of the absorption of 

 any matter. So it may possibly be in the case of the carbonate of 

 ammonia. As, however, the aggregation caused by this salt travels 

 down the tentacles at a quicker rate than 'when insoluble par- 

 ticles are placed on the glands, it is probable that ammonia in 

 some form is absorbed not only by the glands, but passes dpwn 

 the tentacles. 



Having examined a leaf in water, and found the contents of 

 the cells homogeneotis, I placed it in a few drops of a solution of 

 one part of the carbonate to 437 of water, and attended to the cells 

 immediately beneath the glands, but did not use a very high power. 

 No aggregation was visible in 3 m.; but after 15 m. small spheres 

 of protoplasm were formed, more especially beneath the long-headed 

 marginal glands; the process, however, in this case took place with 

 unusual slowness. In 25 m. conspicuous spherical masses were 

 present in the cells of the pedicels for a length about equal to that 

 of the glands; and in 3 hrs. to that of a third or half of the 

 whole tentacle. 



If tentacles with cells containing only very pale pink fluid, and 

 apparently but little protoplasm, are placed in a few drops of a 

 weak solution of one part of the carbonate to 4375 of water (1 

 gr. to 10 oz.), and the highly transparent cells beneath the glands 

 are carefully observe*! under a high power, the.se may be seen 

 first to become slightly cloudy from the formation of numberleM^ 



