68 ON THE STRUCTURE OF THE ROOT. 



therefore, enquire into the structures by which this food material 

 is carried downwards in the root. 



We have, therefore, in the examination of a typical root, to 

 see if we can determine by what special structures, if any, the 

 following kinds of work are done : — 



I. — Fixture and support of plant. 



2. — Absorption of water. 



3. — Conduction of water and food upwards. 



4. — Conduction of food materials downwards. 



We may obtain roots for examination in two ways. We may 

 dig up roots growing in the soil, or we may plant seeds in sawdust 

 and use the coots of the seedlings. The latter is the simpler and 

 for many purposes the best method, as it is often difficult to clear 

 roots obtained in the former way of all the particles of soil that 

 adhere to them. As, however, the roots of seedlings have been 

 well described in text-books, I propose to take a root that is not 

 so well known, namely — that of the Common Lime, Tilia Europea. 



The material is best obtained by digging up roots of a lime, 

 and selecting those roots which have not had their apices broken 

 off. Let us take one of the branches about the size of a knitting 

 needle and examine its appearance. It is brownish in colour, and 

 should possess a somewhat rounded tip. Some two or three inches 

 behind the tip, lateral branches, rootlets, will be seen, light in 

 colour and much smaller than the main root. About half an inch 

 behind the apex of the root, there is a slight expansion of the 

 root, covered by particles of soil which are rather difficult to rub 

 off. This bulging portion extends for perhaps half-an-inch along 

 the root. On washing it carefully in water, it will be found to be 

 covered with delicate white hairs — the root-hairs — through which 

 the absorption of water takes place. Notice how firmly the par- 

 ticles of soil stick to them, so that the hair is often torn on trying 

 to rub the soil away. This is due to the fact that the surface of 

 the hair often becomes transformed into a kind of jelly, in which 

 particles of soil get embedded. These particles become decom- 

 posed and the mineral substances contained in them dissolved, 

 partly owing to the secretion of an acid by the root-hairs, and the 

 solution thus obtained is then absorbed. 



Between the hairs and the root-tip, a clear space exists, deli- 



