see 
Cuar. III.) THE PROCESS OF AGGREGATION. 51 
and after 3 hrs. the cells of all the tentacles were affected for 
one-third or one-half of their entire lengths. Hence there 
can be no doubt that the exposure of leaves to carbonic acid 
either stops for a time the process of aggregation, or checks 
the transmission of the proper influence when the glands are 
subsequently excited by carbonate of ammonia; and this 
substance acts more promptly and energetically than any 
other. It is known that the protoplasm of plants exhibits 
its spontaneous movements only as long as it is in an 
oxygenated condition ; and so it is with the white corpuscles of 
the blood, only as long as they receive oxygen from the red 
corpuscles ; * but the cases above given are somewhat different, 
as they relate to the delay in the generation or aggregation 
of the masses of the protoplasm by the exclusion of oxygen. 
Summary and Concluding Remarks.—The process of aggre- 
gation is independent of the inflection of the tentacles and 
apparently of increased secretion from the glands. It 
commences within the glands, whether these have been 
directly excited, or indirectly by a stimulus received from 
other glands. In both cases the process is transmitted from 
cell to cell down the whole length of the tentacles, being 
arrested for a short time at each transverse partition. With 
pale-coloured leaves the first change which is perceptible, 
but only under a high power, is the appearance of the finest 
granules in the fluid within the cells, making it slightly 
cloudy. These granules soon aggregate into small globular 
masses. I have seen a cloud of this kind appear in 10 s. 
after a drop of a solution of carbonate of ammonia had been 
given to a gland. With dark red leaves the first visible 
change often is the conversion of the outer layer of the fluid 
within the cells into bag-like masses. The aggregated 
masses, however they may have been developed, incessantly 
change their forms and positions. They are not filled with 
fluid, but are solid to their centres. Ultimately the colourless 
granules in the protoplasm which flows round the walls 
coalesce with the central spheres or masses; but there is still 
a current of limpid fluid flowing within the cells. As soon 
as the tentacles fully re-expand, the aggregated masses are 
* With respect to plants, Sachs, ‘Quarterly Journal of Microscopical 
‘Traité de Bot. 3rd edit., 1874, Science, April 1874, p. 185. 
p- 864. On blood corpuscles, see 
E 2 
