SCIENCE-GOSSIP. 



STRUCTURE AND GROWTH OF THE CELL-WALL. 



By Arthur J. Maslkn. 



HTHE cellular structure of plants was first de- 

 scribed by Robert Hook about the middle of 

 the seventeenth century. He distinguished between 

 the hollow spaces and the dividing walls, to the 

 former of which he gave the name of cells. But 

 he really does not appear to have seen very much. 

 A little later two anatomists, Malpighi and Grew, 

 studied the subject and published figures of cells, 

 and to their work must be attributed the foundation 

 of our knowledge, although their works had but little 

 resemblance to modern descriptions of vegetable 

 anatomy. Thus, Grew conceived of the walls of 

 all cells being composed of an extremely fine web. 

 They both combined the physiological considera- 

 tion of the functions of organs with the examination 

 of their structure. But they did investigate the 

 cell-wall. The subject lay practically dormant 

 from Malpighi and Grew to the beginning of the 

 present century, excepting, perhaps, Wolff (1733- 

 1794), who pointed out that but one cell-membrane 

 lies between two adjacent cells, a point which 

 succeeding anatomists were a long time in 

 determining. 



At the beginning of the present century the 

 subject was investigated by a Frenchman, Mirbel, 

 and he made the first important contribution to 

 our knowledge from several points of view, and his 

 ideas agreed in the main with those of Wolff. An 

 important discovery was made in the second 

 decade of this century by the younger Moldenhawer, 

 who succeeded in isolating the cells of tissues by 

 boiling and macerating in water (181 2). This 

 brought him into direct antagonism with Mirbel as 

 to the structure of the cell-wall. He found that 

 the cells and vessels were closed tubes and sacs 

 after isolation, and must necessarily, as it would 

 seem, so lie one against another in the living plant, 

 that the wall between every two spaces is formed of 

 two laminae. He also conceived of the cell-wall being 

 a sort of lacework. The younger Moldenhawer 

 may be taken as closing the first section of this 

 century, during which time he had improved the 

 methods of observation, compared his own observa- 

 tions with those of others with great acuteness of 

 judgment, and did all that could be expected with 

 the instruments of his time. 



From 1812 to 1828 no important advance was 

 made, although great improvements were made in 

 the compound microscope, thus enabling succeed- 

 ing observers to have the advantage of improved 

 instruments. Now we come to Von Mohl, a man 

 intimately acquainted with all branches of botanical 

 science, many of which he materially advanced. 

 He made the solid framework of cells the object of 



special and searching examination, and he never 

 forgot that the interpretation of visible structure 

 must not be disturbed by physiological views. 

 His views on growth in thickness of cell-mem- 

 branes and the sculpture caused by it was published 

 in 1828. He conceives of all organs being originally 

 formed of thin-walled closed cells, which in the 

 tissues are separated by walls formed of two 

 lamellae on the inside of which new layers were 

 formed which lie one upon another and represent 

 the secondary thickening layers, whilst on the 

 inner side of the membrane thus thickened by 

 apposition there may (in some cases) be seen a 

 tertiary layer. He also supposed that pits and 

 spiral and other thickening was due to deposition 

 of thickening material locally on the inside of the 

 originally smooth thin cell- wall. 



Von Mohl also definitely called the layer which 

 gives way when a tissue is macerated, the inter- 

 cellular substance, although he afterwards aban- 

 doned this more and more until he limited its 

 occurrence to certain cases only. 



Coming now to what we may call the more 

 modern views of cell-thickening and growth we 

 reach Nageli. Following naturally from Nageli's 

 conception of the micellar structure of protoplasm, 

 which he considered to be made up of crystalline 

 groups of molecules, to which he gave the name of 

 micellae, and which are always separated from one 

 another by water. The distance between the 

 micellae varies ; when water is given off the micellae 

 come closer together, and vice versa. On this 

 conception has been based the intussusception 

 theory of the growth of the cell-wall. 



The intussusception theory holds that the 

 crystals (micellae) can be moved about, get farther 

 apart, etc., and fresh cellulose micellae are inter- 

 calated between those already present (accom- 

 panied by increase in size of the micellae already 

 present), forcing them apart, and thus the wall 

 grows both in surface and in thickness. On 

 examination of the cell-wall in section, it is seen to 

 be made up of concentric layers, to which was 

 given the name of stratification (Schichlung). In 

 surface view the cell -walls are seen to have fine 

 lines running across them, often crossing one 

 another at right angles. This is striation 

 (Streifung). 



Nageli viewed these appearances as the optical 

 expression of watery or less watery layers. 



According to his view there is no reason why the 

 striation lines of one and the same lamella could 

 not cross one another. This was one of the fatal 

 things that upset his theory. We do not have two 



