September 21, 1905 J 



NATURE 



519 



the discussion. Mr. Sydney F. Wallier read a paper on 

 earth in collieries, in which he pointed out some of the 

 difficulties in carrying out the special rules drawn up by 

 the departmental committee for the installation and use 

 of electricity in mines. If earth was to be admitted into 

 the system, the only method of carrying out the wishes 

 of the committee was to use an uninsulated return com- 

 pletely enclosing the live conductor. The last paper read 

 was by Mr. John T. Stobbs on the value of fossil Mollusca 

 in Coal-measure stratigraphy. He expressed the opinion 

 that Mollusca afforded the best means of correlating Coal- 

 measures, and considered that their neglect was due to 

 inadequate collections in public museums, and to the fact 

 that teachers failed to impress upon students the utility 

 of the Mollusca as zonal indices. The Coal-measures were, 

 he thought, comparatively neglected by the geologist, the 

 knowledge of the Ordovician, Silurian, and Chalk systems 

 being much more e.\act than that of the 3000 feet of Coal- 

 measures. The remaining days of the meeting were 

 devoted to excursions to Chanters Colliery, to New Moss 

 Colliery, to the Manchester Museum, to the works of the 

 British Westinghouse Company and the Manchester Ship 

 Cinal, to Pendleton Colliery, and to other places of 

 interest. 



THE BRITISH ASSOCIATION. 

 SECTION K. 



Opening Address' by Harold Wager, F.R.S., H.M.I., 

 President of the Section. 



On some Problems of Cell Structure and Physiology. 

 Introiuction. 



When Robert Hooke, in the early part of the seven- 

 teenth century, discovered, with the aid of his improved 

 compound microscope, the cell structure of plants, he 

 little thought that our ultimate knowledge of the physical 

 and chemical processes in the living organism, of its 

 growth and reproduction, of the problems of heredity and 

 of the factors underlying the origin of life itself, would 

 be in the main dependent upon a clear understanding of 

 the structure and physiology of the cell. 



Hooke 's researches did not, in fact, carry him very far, 

 and we must turn to the nearly contemporaneous works 

 of Malpighi and Grew on the anatomy of plants for the 

 first clear indication of the important part which cells 

 take in the constitution of the various tissues of plants. 

 The account they give of them is extremely interesting 

 in the light of our present knowledge. Grew, for example, 

 in speaking of the structure of the root, compares the 

 parenchyma to a sponge, " being a body porous, dilative, 

 and pliable ... a most exquisitely fine wrought sponge." 

 The pores are spherical and consist of " an infinite mass 

 of little cells or bladders. The sides of none of these are 

 visibly pervious from one into another ; but each is bounded 

 within itself. . . . They are the receptacles of liquor, 

 which is ever lucid, and . . . always more thin or 

 watery." There is no indication either in Grew's or 

 Malpighi's works that they understood the significance 

 of this cell structure, and it was not until the beginning 

 of the nineteenth century, after a lapse of some 150 years, 

 that any insight into the real nature of the cell and its 

 functions was obtained. But then began a period of 

 activity — associated with the names of Turpin, Meyen, 

 Robert Brown, Purkinje, J. Miiller, Henle, Valentin, and 

 Dutrochet — which culminated in the cell theory of Schleiden 

 and Schwann that the common basis of all animal and 

 plant tissues is the cell, and that it is upon this elementary 

 vital unit that all growth and development depends. 



The nucleus was discovered in 183 1 by Robert Brown 

 in various tissues of the Orchidese and in some other 

 families of the monocotyledons, as well as in some 

 dicotyledons. He described it as a " single circular 

 areola, generally somewhat more opaque than the mem- 

 brane of the ceil," and more or less granular. It is very 

 distinct and regular in form, and its granular matter is 

 held together by a coagulated pulp not visibly granular, 

 1 Slightly abridged. 



NO. 1873, VOL. 72] 



or, which may be considered equally probable, by an 

 enveloping membrane. Although Robert Brown was the 

 first to recognise the importance of the nucleus, and to 

 give it a name, it had been seen by previous observers, 

 and he himself mentions that he had met with indications 

 of its presence in the works of Meyen and Purkinje, 

 chiefly in some figures of the epidermis ; in a memoir by 

 Brogniart on the structure of leaves, and that Mr. Bauer 

 had particularly noticed it in the cells of the stigma of 

 Bletia tankervilliae , but had associated it with the im- 

 pregnation by pollen. There are some figures by 

 Leeuwenhoek, published in 1719, to which Prof. L. C. 

 Miall has directed my attention, of blood-corpuscles of 

 a fish, human epidermal cells, and the connective tissue 

 of a lamb, in which nuclei are shown, and they had been 

 seen by Fontana (1781) in epithelial cells, and by Cavolini 

 (1787) in some fishes' eggs. 



To Schleiden and Schwann the cell was essentially a 

 membranous vesicle enclosing a fluid sap and a solid 

 nucleus. They thought that it arose in contact with the 

 nucleus as a delicate transparent vesicle which gradually 

 increased in size and became filled with the watery sap. 

 As soon as it was completely formed, the nucleus, having 

 done its work, was either absorbed or cast off as a " use- 

 less member," or in some cases was " found enclosed in 

 the cell-wall, in which situation it passes through the 

 entire vital process of the cell which it has formed." So 

 far from being the most important organ of the cell, as 

 we now consider it to be, they saw in the nucleus merely 

 a centre of cell formation which is no longer required 

 when the cell is formed. It was left for Hugo von Mohl 

 to show that the mucus-like contents of the cell which 

 he called protoplasm (1846) is the real living matter in 

 which reside those activities which call into play the 

 phenomena of life, and that the origin of nuclei by division 

 from a nucleus already existing in the parent cell would 

 possibly be found to occur very widely. Von Mohl, 

 Nageli, and Hofmeister all appear to have had some 

 idea of the importance of the nucleus in cell division. 

 Von Mohl says that the " process is preceded in almost 

 all cases bv a formation of as many nuclei as there are 

 to be compartments in the mother-cell." Hofmeister 's 

 description of it is interesting : " The membrane of the 

 nucleus dissolves, but its substance remains in the midst 

 of the cell ; a mass of granular mucilage accumulates 

 around it : this parts, without being invested by a mem- 

 brane, into two masses, and these afterwards become 

 clothed with membranes and appear as two daughter- 

 nuclei." 



It is, however, mainly to the researches of the last 

 thirty years that we owe our knowledge of the many 

 complex cell-activities at work in living organisms, and 

 we are still only just on the fringe of the great problems 

 which cytologv has to solve. Some of the most important 

 of these are the origin and evolution of the nucleus,^ the 

 meaning of the complex mode in which the nucleus divides, 

 the origin and nature of the spindle figure and centro- 

 somes, the part played by the chromosomes in the trans- 

 mission of hereditary characteristics, the meaning of the 

 phenomena accompanying fertilisation, the significance of 

 the longitudinal division of the chromosomes and of their 

 reduction in number in the sexual cells, and the evolution 

 of the living substance. The satisfactory solution of these 

 problems depends upon a clear understanding of the struc- 

 ture of protoplasm and its various differentiations. How- 

 far we have succeeded in obtaining this I will endeavour 

 to show. 



The Differentiation of Structure in the Cell. 



The essential constituent of a cell is the protoplasm. 

 This is differentiated into two constituents, the cytoplasm 

 and the nucleus. It is usually held that this differentiation 

 is an essential one, and tha't these two constituents are 

 present in all cells ; but, as we shall see later, there is 

 some evidence that not only are there cells with very 

 rudimentary nuclei, but cells in which no trace of a nuclear 

 structure can be found at all. 



In addition to this primary differentiation of the cell, 

 secondary differentiations occur, resulting in the produc- 

 tion of organs such as chloroplasts, chromoplasts, leuco- 

 plasts, pvrenoids, and pigment spots, which have special 



