CELLULAR TISSUE. 



, 19 ORAXGE. 

 the cell-wall. 



The cells of which it is composed may be either detached wholly or partially (Fig. 

 16), or be more or less conjoined in masses, (Figs. 17 and 18). Their characters are of 

 course the best seen when they are detached from each other. 



The only difficulty, if any, in reference to tissue is in obtaining a correct idea of 

 the simplest of all structures the cell. This may be likened to an orange (Fig. 19), 

 when the rind, a, will correspond to the cell-wall, or boundary of the cell, and the 

 juicy part, b, will represent the contents of the cell. Thus an 

 orange is a cell on a large scale. Or it may be compared to a 

 fowl's egg, when the shell will represent the cell- wall, and the 

 white, with the yolk, the contents of the cell. The egg, therefore, 

 and all similar inclosed bodies, are magnified cells. But the egg 

 has other points of resemblance to the cell. Thus, if the white 

 of the egg be drawn from the shell through a small hole, so that 



the latter shall remain empty (a process very familiar to school- 



, . . 5 ' . . iT _ i, n -. 



boys), we may form a just estimate of the cell-wall as separate b, the contents of the 



from its contents. A cell in botany, therefore, consists of a cell- cel1 ' 



wall and contents, although it be so small as to be undiscernible by the unaided sight. 



"We have already stated that cellular tissue is formed from elementary membrane ; 

 and therefore the cell-wall is nothing more than elementary membrane folded, with 

 the edges adherent together, so as to be able to inclose the contents. 



The contents of cells are, however, of another nature, and are not produced from 

 elementary membrane. They are of three kinds. 1st, a substance lining the inner 



side of the cell-wall, as illustrated 



by the white of egg, and called the 



primordial utricle of Mohl. It is 



well shown by the shading in Fig. 



20, A. This substance is of ex- 



ceeding importance in the develop- 



ment and growth of the cell, and in 



the production of its other contents. 



2nd, a roundish, tolerably - large 



body, or nucleus, or cytoblast, re- 



presented in Fig. 21, b, met with 



in various parts of the cell, but 



usually near to some part of the cell- 



wall. This may be likened to the 



yolk of the egg, and bears the like degree of importance to the 



other parts of the cell that the yolk bears to the egg. 3rd, cer- 



tain lesser bodies varying in size, shape, and number, termed 

 nucleoli, formed within the nucleus. 



It appears that the nucleus is a central point of all actions proceeding within the 

 cell, but that the primordial utricle is the efficient agent. All these parts may be fami- 

 liarly and readily observed in the common strawberry (Fragaria), or the mistletoe berry 

 (Visctim album), or any other juicy fruit. "We assume that our readers have a small 

 microscope of some kind, which may be obtained for a sum varying from 2 to 

 4 of any respectable optician, with pieces of glass and other apparatus needful 

 for microscopic observation. Take then, with the point of a needle, a piece from the 

 centre of the strawberry, not larger than a pin's head; place it in the glass slide, 



Fipr. 20. Cell after 

 Unger. The out- 

 lines, C, are intend- 

 ed to represent the 

 boundary of the cell, 

 or the cell-wall. 



B is the central nu- 

 cleus or cytoblast. 



A, the lining of the 

 cell-wall or the pri- 

 mordial utricle of 

 Mohl. 



21. Cells from the flower- 

 ing stem of the leek (Allittm 

 Porrum), showing at athe cell- 

 wall, and at b the nucleus 

 and the nucleoli. The other 

 contents of the cell are trans- 

 parent. 



