\'0L. 43 TORREYA Jilv 1943 



Cell Division as a Problem of Pattern in Plant Development* 



Edmund W. Sinnott 



The plane in which a cell divides and the position of the new wall laid 

 down between the two daughter cells involve important problems, not alone 

 as to the behavior of individual cells, but also as to the development of multi- 

 cellular plant structures, since the planes of division in a mass of growing 

 tissue must evidently be related to the direction in which growth occurs, and 

 thus to the form of the organs produced. 



Various hypotheses have been suggested as to factors which determine 

 the position of the new wall in a dividing cell. Hofmeister showed that such 

 walls are usually formed at right angles to the longer dimensions of the cell. 

 Sachs observed that a new wall tends to meet the old one at right angles. The 

 direction of mechanical pressure, light, electrical currents, and gradients 

 of various chemical substances have been shown to affect the orientation of 

 the division wall. Errera and Berthold, later supported by D'Arcy Thompson 

 and others, maintained that since cell walls in embryonic tissues are thin 

 and semi-liquid, their position is governed by molecular forces and will be 

 such that minimum surface and maximum stability result, so that no more 

 than three walls meet at one point. All these "rules"' can be abundantly illus- 

 trated from plant material, but every histologist has seen exceptions to them. 

 Some of these have recently been discussed by the writer and Dr. Bloch. 

 The problem is evidently too complex to be explained by any one hypothesis. 

 It has too often been approached simply as a question relating to the activity 

 of single cells rather than of these cells as members of an organized multi- 

 cellular system. The present paper reports a study of cell division as it occurs 

 in a simple plant structure, in an attempt to determine what relation there may 

 be between the manner in which a cell divides and the position which it 

 occupies in such an organized entity. 



The shoot axis of Eqnisetinn provides particularly good material for 

 such a study. Its growth is centered in a single apical cell and the lineages 

 of cells arising from this are relatively easy to follow. The structure of the 

 axis is without serious complication and the leaves are small, simple and in 

 whorls. A number of previous studies have been made on various species of 

 this genus and for many of them the development of the shoot apex is well 

 known. It seems worth while, however, to examine the facts for a single 



* Presented at the 75th Anniversary Celebration of the Torrey Botanical Club at Colum- 

 bia University, Monday, June 22, 1942. 



The writer wishes to express sincere appreciatian to his colleague Dr. Robert Bloch. 

 who carried out the technical part of the study here reported and prepared the illustration- 



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