14 



CELLULAR TISSUE. 



Fig. 41. Fibre cell from the leaf 

 of the PLECROTHALLIS, having a 

 single fibre. 



in which sections of tone are prepared for examination, It is impossible to 



examine these interesting structures, and to observe 



how admirahly they are adapted to give strength and 



power of resistance to parts which pre-eminently 



require it, without being reminded of the great 



similarity between them and bone cells in the bones 



of animals. There are, however, several points of 



dissimilarity; and, amongst others, that the cell- 

 wall, which is retained in thick-walled cells, is lost 



in bone cells. 



Fibre Cellular Tissue This form of cell 



is marked by having one or more fibres wound in 



a spiral direction on its inner side (Figs 41 & 43). ri 40 . _ Concentric laycr , of Sclero . 



The fibre may be loose in the cell, as in the Opuntia gen j n ^ ce n s of the bark of tue 



vulgaris (Fig. 42), where it is flat, or in the elongated BEECH TREE (Fagus). 



cell of the hairs on the seed of the Cottomia grandiflora, or of the common sage, where 

 'it is round. 



We have already re- 

 ferred to elementary fibre 

 (p.7); and have only further 

 to remark that it obtains 

 its spiral direction by the 

 growing process being car- 

 ried on at the free end, 



hilst the other part of the fibre is attached to the mem- 

 brane. In this mode the 

 resistance is unequal, and 

 a circular or spiral direc- 

 tion is given to the new 

 structure. This form of 

 cell is very abundant, and 

 is probably more or less 

 filled with air, since the 

 inclosed fibre is well fitted 

 to prevent the collapse of 

 the two sides of the cell. 



It is usual to find the 

 cells not isolated, but in 

 clusters, and oftentimes 

 arranged in masses with 



much symmetry, as may be seen in the drawing (Fig. 44) of the fibro- cellular tissue 



lying in situ in the leaf of the Pleurothallis. 



There is no [structure in animals corresponding with the nbro-eellular tissue in 

 vegetables ; but cellular tissue in the simple form is exceedingly abundant, and, in the 

 form of fat cells (Fig. 45), bears great resemblance to cells of vegetable origin. It is 



also an interesting fact that the cartilage of the ear of the rat and mouse (Fig. 46), and 



mere particularly of the rudimentary spinal column of the lamprey, is so modified 

 as almost exactly to simulate a vegetable cell. 



Fi 



Fig. 42. Fibre cell from the 

 OPUKTIA VTJLGARIS, show- 

 ing a flattened fibre lying 

 detached from the cell- 

 wall. 



43. Fibre cell from the 

 leaf of an ORCHIS (Saccola- 

 bium guttatum), having seve- 

 ral fibres wound in opposite 

 directions. 



