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On the Structure and Division of the Vegetable Cell. 



By W. H. Gilburt, F.R.M.S. 



(Read Nov. 25, 1881.) 

 Plate I. 



Schleiden, who was the founder of what is known as the " Cell 

 theory," defines the vegetable cell as "the elementary organ which 

 constitutes the sole essential form-element of all plants, and with- 

 out which a plant cannot exist," and as consisting, when fully 

 developed, of "a wall composed of cellulose, lined with a semi-fluid 

 nitrogenous coating." With him, therefore, a cell consisted of two 

 elements only, a closed vesicle, with a wall more or less firm, and 

 its semi-fluid parietal lining. In the year 1833, however, a third 

 element was added by Robert Brown, who first observed and 

 described the nucleus in certain Orchids ; and Schleiden subse- 

 quently pointed out its regular occurrence in at least the young 

 cells of all flowering plants. He also discovered in it a denser 

 body, which may, however, be sometimes absent, the Nucleolus. 



Here then we have the idea of a cell as a threefold structure, 

 the cellulose wall, the semi-fluid contents, and the nucleus, to the 

 second of which Von Mohl gave the name of protoplasm. 



This conception of the nature of the vegetable cell is the one 

 which is still most commonly held, and each of its component 

 parts is generally regarded by those who have only a general 

 knowledge of the subject as of equal value. 



A little consideration will, however, show that such a view does 

 not fully represent the facts of the case, for if we regard the 

 cellulose wall as an essential part of a cell, we exclude some of the 

 most important protoplasmic structures which are developed dur- 

 ing the life of a plant. For instance, the contents of the young 

 embryo-sac of a flowering plant consists of a mass of protoplasm 

 with a nucleus. During the period of the growth of the ovule 

 this nucleus divides, giving rise to two daughter nuclei ; in these 

 secondary nuclei division again takes place. Thus we have four, 

 all embedded in the general protoplasm of the embryo-sac, two 

 being placed at each pole. Division again takes place in the 



