Nov. 25, 1S80] 



NATURE 



79 



organised plants. Niigeli showed, for instance, that since 

 in a unicellular alga (Cauh-rpa) a morphological ditTeren- 

 tiation of root, stem, and leaf is indicated, morphological 

 is not dependent upon histological differentiation. He 

 discovered also that in the organs of certain cryptogams 

 growth is effected by the repeated segmentation of a single 

 apical cell, and that this segmentation may take place 

 always in one plane only {DLlcsscria), or in two or three 

 planes (stem of Echinomitiitoii, PJutsciiiu, Jungcrinannia, 

 leaves of mosses). 



In the following year (1S47) he published his work on 

 " The Classification of the Algae " (" Die Neueren Algen- 

 systeme"), which is of great value, partly on account of the 

 acute criticisms on the various proposed classifications of 

 this group of plants which it contains, but more particu- 

 larly on account of the number of new facts concerning 

 their structure and life-history which are contributed. 

 The descriptions of Valonia, Udotea, and Acctabtilaria 

 may be especially mentioned : it is shown that they have 

 essentially the same structure as Caulerpa. The same 

 praise may be awarded to another work, "The Genera of 

 Unicellular Alga;," which appeared two years later. 



The next publication of importance was the first number 

 of the PJlanscnphysiologischc Untcfsiuhiini^cn, and the 

 most interesting of the papers which it contains is the one 

 on the Primordial Utricle. Attention is directed to its 

 presence in all living cells, to its influence upon the 

 osmosis of substances in solution into or out of the ceil, 

 and to its activity in forming the cell-wall; in short, it is 

 clearly shown to be the living portion of the cell. The 

 second number did not appear until 1S58, although the 

 MS. was ready in 1S55, the delay being due principally 

 to Nageli's removal from Freiburg to Zurich, and then 

 again from Ziirich to Munich on his acceptance of the 

 Professorship of Botany in that University. Although it 

 must have been vexatious, still the delay enabled Xageli 

 to extend his researches in various directions and thus 

 contributed materially to make the great work on starch- 

 granules one of the most complete monographs which 

 was ever written on any subject. This second number 

 is entirely taken up by this work, which gives an account 

 of these bodies, including their structure, development, 

 chemical composition, and physical properties, as well as 

 their distribution in plants. It is a monument of patient, 

 accurate investigation, devoted to a subject which appears, 

 at first sight, to be of limited interest, but which ultimately 

 suggested one of the most remarkable generalisations of 

 modern times, namely, what is known as Nageli's theory 

 of the structure of organised bodies. The primary fact 

 upon which this theory is based is the property which 

 starch-granules have of swelling-up — that is, of absorbing 

 a certain amount of fluid with a consequent increase of 

 bulk — when treated with certain reagents (dilute acids 

 and alkalies), and of diminishing in size in consequence of 

 a loss of water when treated with other reagents (alcohol). 

 From these phenomena he inferred that the starch-granule 

 consists of solid particles, which are impenetrable by water, 

 but which are capable of taking up a certain amount of 

 water between them, and that the amount of this water 

 may vary according to circumstances. When the granule 

 is absolutely dry, these solid particles — to which he gave 

 the name of iiwlecitles — apparently come into perfect 

 contact, for the granule does not lose its transparency, 

 which would be the case if air were included in its 

 substance. 



It may be remarked here parenthetically that the word 

 ■molecule used by Nageli to designate these solid particles 

 has not the same sense as it has when it is used in 

 chemistry ; one of these molecules is probably an aggre- 

 gation of chemical molecules. In order to avoid any 

 possible confusion on this score Nageli has substituted 

 the word micella for molecule in his more recent works. 

 The forces by which these micclLT, with their surrounding 

 watery areas, are held together are, firstly, the attraction 



imbibition will be reached w-hen 



As to the 



existing between the micella; ; and secondly, the attraction 

 which exists between each micella and the water which 

 surrounds it ; the latter of these attractions must neces- 

 sarily be greater than the former, but whereas the former 

 varies inversely as the square of the distance, the latter 

 must vary inversely as some higher power. Thus, if A 

 represent the attraction between two micella;, D the 

 attraction between a micella and the water, and D the 

 distance between two micell;e, the limit of swelling-up or 

 B _ A_ 

 /)=+-' />-■' 



form of the micella;, it is evident that they are not 

 spherical or oval, for in that case the starch- granules 

 would necessarily contain air when dry, and further, the 

 denser parts of them would have to contain at least 26 

 per cent, of water, whereas, as a matter of fact, they only 

 contain 14 per cent. They must be therefore more or less 

 polyhedral, but they are not equiaxial since the swelling-up 

 does not take place equally in all directions. 



By this theory it was found possible to explain satis- 

 factorily certain difficult points of structure, such, for 

 instance, as the stratification of starch-granules and the 

 slriation and stratification of cell-walls. All these depend 

 upon the alternation, in one or more planes, of dense and 

 less dense layers. The proportion of solid to fluid is 

 greater in the dense than in the less dense layers, or, in 

 the terms of Nageli's theory, the relative size of the 

 micellre to the watery areas surrounding them is greater 

 in the layers of greater density. Further, this theory 

 affords a satisfactory explanation of the mode of growth 

 of a cell-wall. It is easy to understand that when the 

 limit of extensibility is nearly reached— that is, when the 

 micella; of the membrane are separated as far as possible 

 —new micelke can be deposited in the interstices, the 

 extended condition of the membrane being thus rendered 

 permanent. This mode of growth is commonly known 

 as growth by intiissusceplion. 



This is the stage to which the development of the 

 theory is brought in this work. In the year 1S62 Nageli 

 published a paper in the Proceedings of the Bavarian 

 Academy on the " .\pplication of Polarised Light to the 

 Study of the Structure of Plants," which advanced it very 

 considerably. He found, in the first place, that organised 

 stiuctures, such as starch-granules or eel!- walls, are 

 doubly refractive, and that this property is not aftected 

 by causing them to increase or diminish in size in conse- 

 quence either of the absorption or removal of water, or by 

 mechanical stretching or pressure. From this he con- 

 cluded that the double refraction is not a property of the 

 organised structure as a whole, but that it belongs to each 

 individual micella : hence these micella: must be crystal- 

 line. Again, from the interference colours which these 

 objects present when examined with polarised light, he 

 ascertained that the crystalline micella; have three axes 

 of elasticity, that they must be bi-axial crystals ; and 

 further, by comparing the effect produced by the 

 passage of polarised light through glass under various 

 degrees of pressure, he arrived at the conclusion that the 

 micella" are so arranged in the membrane of which they 

 form part that one of their axes of elasticity is perpen- 

 dicular to the surface, whereas the other two axes lie in 

 the plane of the membrane. In a subsequent paper con- 

 tained in the same periodical, he shows that the crystals 

 of proteid substance, which oecur in various seeds and 

 tubers, have the same molecular constitution as starch- 

 granules and cell-walls. By dose and acute reasoning 

 from carefullv observed facts, Nageli has therefore suc- 

 ceeded in establishing this theory of the molecular consti- 

 tution of organised bodies, a theory which satisfactorily 

 explains many of the peculiarities of structure and 

 properties which they present. There can be little doubt 

 that it is justifiable to extend this theory to the explanation 

 of the intimate structure of protoplasm ; in fact, in his 

 later publications Nageli has asserted as much, and in 



