CONDITION OF AGGREGATION OF ORGANISED STRUCTURES, 669 



a violent swelling takes place in cellulose and starch-grains, and they pass into a pasty 

 state. Protoplasmic substances, on the contrary, coagulate, as they do under the in- 

 fluence of higher temperatures. Concentrated sulphuric acid finally completely destroys 

 the micellar structure of both with a smaller or larger amount of chemical change, and 

 they deliquesce. 



(c) Solution of Potash acts on starch-grains like sulphuric acid, especially in causing 

 them to swell up. Its action on protoplasmic substances is on the other hand very 

 different from that of acids ; if the solution is dilute they swell up strongly or deliquesce, 

 and this is especially the case with protoplasm and the nucleus of very young cells (the 

 nuclei of older cells often resist the action strongly). But in a highly concentrated 

 solution of potash protoplasmic structures often retain their form and apparently their 

 structure ; they neither coagulate nor deliquesce. The fundamental destruction of their 

 micellar structure which has nevertheless taken place is evident from the fact that they 

 immediately deliquesce if water is added copiously. 



(d) Mechanical Influences. Organised structures bear without injury mechanical forces 

 such as pressure, impact, or slight traction ; they are either sufficiently elastic, like starch- 

 grains and cell-walls, again to bring into equilibrium the changes which are thus caused 

 in their internal tension and external form ; or they are inelastic like protoplasm and 

 chlorophyll-granules, and can then equalise small passive changes of form in another way. 

 But stronger forces cause disruptions of the micellae which cannot be again effaced. 

 The micellar structure of the separated portions may however still be perfectly retained, 

 as is shown by fragments of starch-grains and cell-walls. This is still more evident 

 in motile protoplasm, where the separated portions of the previously continuous sub- 

 stance behave like so many individuals, and have the power of independent motion ; 

 as, for example, separated portions of plasmodia, the detached halves of the rotating 

 protoplasm in the root-hairs of Hydrocharis when contracted by a solution of sugar, &c. 

 In the same manner two or more separated portions of protoplasm may unite into a 

 whole, as in the formation of large plasmodia and of zygospores, the fertilisation of 

 oogonia, &c. The only purely mechanical mode in which complete destruction of an 

 organic structure can be accomplished is by crushing ; /. e. by complete disseverance 

 of its micellae and their subsequent promiscuous intermixture. In this case a chemical 

 change usually directly follows the mechanical destruction of the micellar structure of 

 the protoplasmic substance. In some cell-walls the mere interruption of continuity by 

 a cut causes striking changes in the adjoining and the more distant parts ; thus, accord- 

 ing to Nageli, cell- walls of Schi%omeris that have been cut through become shorter and 

 thicker to a remarkable extent. 



{e) Changes in the micellar structure of organised structures caused by injurious 

 influences determining their death are often accompanied by striking changes in their 

 relations to diffusion. With respect to starch and cellulose but little is known in this 

 respect ; but the phenomena connected with protoplasm, including the nucleus, are very 

 remarkable \ Normal living protoplasm does not, for example, absorb any colouring 

 material from the surrounding solution ; but as soon as it has been killed by heat or by 

 a chemical reagent, the dissolved colouring material not merely penetrates into it, but 

 accumulates in it to such an extent that the dead protoplasm appears of a much deeper 

 colour than the surrounding solution of the colouring substance. Starch and cellulose, 

 on the contrary, even in a fresh unchanged condition, absorb from a solution of iodine 

 a comparatively much larger quantity of iodine than of the solvent, and become of a 

 much deeper colour than the surrounding solution ; the colour is also different, usually 

 blue, while the surrounding solution is yellowish brown. The protoplasm which fills the 

 cells and has been killed in any manner, by frost, heat, or chemical agents, is more 



* Nageli, Pflanzenphysiologische Untersuchungen, vol. I. p. 3 et s^g-.— Hugo de Vries, Sur la 

 permeabilite du protoplasm des betteraves, Arch. Neerland. vol. VI, 1871 : [also id., Unters. ueb. 

 die Mechanischen Ursachen der Zellstreckung, i87jf. — PfefTer, Osmotische Untersuchungen.] 



