24 



THE ELEMENTARY STRUCTURE OF PLANTS. 



closed partitions ; forming a structure not unlike a honeycomb. 

 This is also shown by the fact, that the liquid contained in a juicy 

 fruit, such as a grape or currant, does not escape when it is cut in 

 two. The cavities being called CELLS, the tissue thus constructed 

 is termed CELLULAR TISSUE. When the body is sufficiently trans- 

 lucent to be examined under the microscope by transmitted light, 

 this structure may usually be discerned without making a sec- 

 tion. We may often look directly upon a delicate rootlet (as in 

 Fig. 1) or the petal of a flower, or a piece of a thin and trans- 

 parent sea-weed, and observe the closed cavities, entirely circum- 

 scribed by nearly transparent membranous walls. 



19. Does this cellular tissue consist of an originally homogene- 

 ous mass, filled in some way with innumerable cavities ? Or is it 

 composed of an aggregation of little bladders, or sacs, which, by 

 their accumulation and mutual cohesion, make up the root or other 

 organ ? Several circumstances prove that the latter is the cor- 

 rect view. 1. The partition between two adjacent cells is often 

 seen to be double ; showing that each cavity is bounded by its 

 own special walls. 2. There are vacant spaces often to be seen 

 between contiguous cells, where the walls do not entirely fit to- 

 gether. These intercellular spaces are sometimes so large and 

 numerous, that many of the cells touch each other at a few points 

 only ; as in the lower stratum of the green pulp of leaves (Fig. 7). 



FIG. 1. Portion of a young root, magnified. 2. A transverse slice of the same, more mag- 

 nified. 3. A smaller vertical slice, magnified. 



FIG. 4. Cellular tissue from the apple, as seen in a section. 5. Some of the detached cells 

 from the ripe fruit; magnified. 



FIG. 6. Portion of a hair from the filament of the Spider Lily (Tradescantia), magnified j 

 c, the cytoblast. 



