THE VEGETABLE CELL. 



125 



of the secondary layers, leaving only minute points of the origi- 

 nal cell-wall bare and transparent. A remarkable variety of 

 the wood-cell is seen in the Pine and Coniferae in general, where 

 the points are targe, transparent, and surrounded by two or 

 three rings. These we call Pitted cells. 



469 



466, Polyhedral cells of parenchyma in pith of Elder. 467, Stellate cells in pith of Rush. 468, Sphericn. 

 ceils in Houseleek. 469. Wood-cells of the Flax fibre. 470. Cellular tissue of a young rootlet. 



377. Spiral cells, where the secondary layer consists of spiral 

 fibres or bands. There may be a single fibre, or several (2 to 

 20) united into a band. It is usually elastic, and may be drawn 

 out and uncoiled. These beautiful cells may be well seen in a 

 shoot of Elder, in the petiole of Rhubarb, Geranium, Strawberry. 

 In the two latter, if gently pulled asunder, the coiled fibres ap- 

 pear to the naked eye. 



378. Annular cells, when there are numerous rings within, 

 instead of a spiral coil, as in the stems of Balsam arid some 

 Cryptogamia. Scalar if orm cells, when the rings seem conjoined 

 by bars crossing between them, giving an appearance compared 

 to a ladder (scala), as in the Vine and Ferns. Porous cells, with 

 the secondary layers full of perforations ; reticulated cells, as if a 

 net-woisk ; and many other forms. 



379. Cellulose, the material of which the outer cell-walls and 

 other secondary layers are made, is proved by chemical analy- 

 sis to consist of three simple elements, carbon, hydrogen, oxy- 

 gen, in the proportions of C J4 H 20 O 20 carbon and the exact 

 elements of water. In the material of the primordial utricle 

 nitrogen is added. Out of these four simple elements (C H O N), 

 with slight additions of lime, silex, and a few other earthy mat- 



