f 



CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 66^ 



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 diniensions 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 Hues 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 w^hen the organic substance has been burnt away. In the 

 same manner a grain of starch leaves behind a skeleton containing very litde solid 

 material when the granulose has been extracted by saliva or some other reagent. 

 From crystalloids also a skeleton in this sense of the term containing very little solid 

 ynatter 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 fojces 



^ Hofmeister (Handbuch der phys. Bot. vol. I. p. 348) has arrived at altogether different 

 conclusions, with which I cannot agree. 



