8 



POPULAR ILLUSTRATIONS OF 



Thirdly : The most important mode of cell-formation carries us a 

 step beyond the cell. The ultimate form of matter, as shown by 

 the highest power of the microscope, exists in atoms called molecules. 

 Under favourable circumstances a group of these molecules form for 

 themselves a covering, or cell-wall. This is called the molecular 

 formation of cells. 



Cells also unite together to form larger cells, and this has been 

 designated the congregation method of increase, and is well exempli- 

 fied in the growth of the lower forms of vegetable life. 



Now cells increasing in one or other of these methods, and 

 becoming united to each other, some of them forming elongated 

 tubes, or, as they are called, vascular organs, and the whole sur- 

 rounded by a delicate membrane or skin, also formed of cells, some- 

 times called " epiblema," constitute and form the roots of plants. 

 The main root of most plants striking from above downwards, gives 



Fig. 4. 



Fig. 3. Grain of wheat germinating a, central root of axis a/, other rootlets covered with 

 hairs 6, plumule -c, cellular sheath or " coleorhiza " covering the axis or base of rootlets 

 d, the seed (after Balfour). 



Fig. 4. Microscopic view of cast of silica in wheat-stem after boiling in nitric acid (after 

 Goadby) a, siliceous plate with serrated edges, which fit in accurately to other plates 

 &, cast of stomata, or breathing-mouth of stem, in flint. 



off numerous branches, the ends of which are formed of cells loosely 

 put together, and thus, having a spongy texture, are called 

 " spongioles," which are, however, covered like the rest of the root 

 or rootlets, with the fine delicate membrane above mentioned. 



It is through this membrane and the spongy texture of the 

 spongioles that all the food of the plant obtained from the soil must 

 pass. It is evident, therefore, that the food must be in a state of 

 solution. 



In the wheat-plant there is no central root. All the rootlets or 



