io8 



MINUTE STRUCTURE. 



[chap. 



Fig. 84. Cellular 

 tissues ; the in- 

 dividual cells 

 oblong, and ar- 

 ranged in verti- 

 cal rows. 



sides when magnified. When you look at the preparation 

 under the microscope, you are pretty sure to find a number 

 of bodies resembhng those represented in 

 the cut. If you do not find them, try ano- 

 ther morsel until you succeed. These bodies 

 are called cells. They are hollow sacs, each 

 filled with fluid. Now, of cells more or less 

 like these, differing principally in size, in 

 relative length and breadth, and in the thick- 

 ness of their sides, eve7'y part of every plant 

 is composed. All the organs are built up 

 of these minute cells. 



3. But take now a very small bit of one 

 of the fibrous strings of the boiled stem. 

 Place it in a drop of water, and, with a couple 

 of needles, one in each hand, separate it into 

 what seem, to the naked eye, to be its constituent fibres, 

 just as you would separate a morsel of string into its finest 

 threads. When you have got it dissected out, put a cover 

 on as before, and examine it under the microscope. You 

 will probably find here, besides numerous cells of various 

 lengths, some long tubes, with their sides {ivalls) curiously 

 marked with delicate fibres, usually arranged in a spiral 

 direction, twisting round and round inside the tube — the 

 coils sometimes very close, sometimes loose ; or you may 

 find the fibre in the form of separate rings in the inside of 

 the tubes. These tubes are called vessels. They originate 

 in this way : A number of cells, such as we saw before, 

 standing one over the other in a row, have the partitions 

 which separate them more or less completely removed, so 

 that the row of cells becomes open all through. We have 

 then a true vessel. Vessels are almost invariably marked 

 either by a spiral, netted, dotted, or ring-like thickening 



