22 W. H. GILBURT OX THE STRUCTURE AND 



regard to the vegetable kingdom ; for Professor Schmitz has been 

 enabled to demonstrate the presence of nuclei in many Thallo- 

 phytes hitherto considered to be destitute of them, and even in 

 plants of so low a type as the Yeast plant; and he concludes "that 

 in all Thallophytes the cells invariably contain one or more 

 nuclei, organisms destitute of a nucleus being altogether un- 

 known."* If, therefore, these observations and conclusions should 

 be confirmed, as in all probability they will, we shall be brought 

 back to the one element of plant structure and life, the cell, as a 

 nucleated mass of protoplasm which may or may not be bounded 

 by a cell-wall. 



Having thus given an extremely brief and, of necessity, very 

 incomplete sketch of the history of the Cell theory, we may now 

 turn to a consideration of its intimate structure as at present 

 known. 



Taking the first, that very generally present, though non- 

 essential, element of cell-structure, the cellulose wall; although 

 there may be nothing either new or very recent to bring before 

 you, yet a brief review of the known facts and present theories 

 concerning it may not be altogether out of place. You will of 

 course know that cellulose is, chemically, a compound isomeric w ith 

 starch, sugar, and inulin,its formula being C 6 H 10 5 . Under the 

 microscope it presents itself normally in young cells as an ex- 

 tremely thin, transparent, homogeneous pellicle. As it becomes 

 older, it increases in thickness, but frequently even in what are 

 commonly spoken of as thin -walled cells, the thickening takes 

 place unequally ; and isolated, or groups of spots remain as thin, or 

 nearly so, as when the wall was first formed, while in still older 

 cells these thin places are sometimes dissolved, and a clear aperture 

 remains between the two adjoining cells. 



Under the highest powers of the microscope nothing which in 

 any true sense can be called structure is to be seen, yet, in common 

 with all matter, we must look upon it as being molecular in com- 

 position, the molecules being solid, isolated particles, between 

 which water penetrates. Now in order to readily understand how, 

 according to present views of growth, the cell-wall increases in 

 superficial area, it is desirable that a clear mental picture should 

 be formed of this molecular structure. True, we cannot give even 

 a rough guess at the extreme minuteness of these component 



* " Journal Royal Microscopical Society, " 1880, p. 438. 



