CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 665 
forced further from one another in certain directions, as is clearly seen upon the 
change of form of the whole, from the formation of fissures, &c. One of the most 
remarkable effects of the tensions thus caused in the interior of the body is the fact 
that when swelling takes place particular dinicnsions may even decrease ; thus, for 
example, the layers of stratification of bast-fibres become very considerably shorter 
when they swell up under the influence of dilute sulphuric acid, the coils of the spiral 
striation becoming closer and larger in circumference. Crystalloids change their 
angles several degrees when they swell. These phenomena are explicable only on 
the supposition that the micellar forces in the interior of organised substances vary 
in intensity in different directions ; and this again is conceivable only on the hypo- 
thesis that the form of the micellae is not spherical. Nageli and Schwendener 
obtained a deeper insight into these laws by a very careful observation of the phe- 
nomena produced by polarised light in cell-walls, starch-grains, and crystalloids \ 
They inferred from these facts a crystalline structure of the individual micellae, and 
that the crystals are doubly refractive and have two optical axes which are so 
arranged, at least in the greater number, that one axis of elasticity within each 
micella of starch-grains and cell-walls is placed radially, but the two other axes 
of elasticity tangentially. In crystalloids the micellae are probably arranged as in 
true crystals, but separated also by layers of water parallel to the faces or lines of 
cleavage. ^ 
The behaviour of chlorophyll-granules and of colourless protoplasm towards 
polarised light, as well as under the addition and removal of water, is at present but 
little known ; and a more definite idea of the form of their micellae is therefore not 
yet possible. 
The solid micellae of one and the same organised body which are separated 
by aqueous envelopes always vary in their chemical nature ; so that at every visible 
point micellae which possess chemically different properties lie by the side of and 
among one another separated by layers of water. In starch-grains, cell-walls, and 
crystalloids this fact is inferred from the circumstance that certain substances are 
extracted by the application of certain solvents, while other substances remain behind, 
constituting what is called the skeleton. This skeleton is of course less dense than 
the original substance ; and it is evident that the extraction has taken place at all 
visible points, without the external form or internal structure having undergone any 
essential change. Thus, for example, a skeleton of cellulose remains behind when 
the lignin has been extracted from wood-fibres by maceration in nitric acid and 
potassic chlorate ; and again, a skeleton of silica remains behind with all the optical 
properties of the cell-wall when the organic substance has been burnt away. In the 
same manner a grain of starch leaves behind a skeleton containing very little solid 
material when the granulöse has been extracted by saliva or some other reagent. 
From crystalloids also a skeleton in this sense of the term containing very little solid 
matter can be obtained by the solution of a part of their substance. The properties 
of these skeletons show that the micellae which remain behind after solution of the 
rest still occupy essentially the same position and are endowed with the same forces 
^ Hofmeister (Handbuch der phys. Bot. vol. I, p. 34S) has arrived at altogether different 
conclusions, with which I cannot agree. 
