128 THE VEGETABLE KINGDOM- 



the following description will therefore apply to vegetables 

 of the more elevated character, such as trees or flowering 

 plants. 



Plants are fixed to the earth, and receive nourish- 

 ment from it by imbibing its liquids, which circulating 

 upwards through the porous structure of the plant itself, 

 and becoming exposed to the air in the leaves, attract to 

 themselves nourishment from that source also. The part of 

 a plant which grows into the earth is called the root; 

 this has a variety of forms, in some it is branched like 

 the upper part, and these branches divide into rootlets 

 or fibres penetrating deep into the ground, and absorbing 

 nourishment in all directions, but this absorption does not 

 take place from the whole surface of the root but from spots 

 covering it, and from the slightly expanded ends of the 

 fibres, these portions are formed of new and porous cellular 

 tissue, and are called " spongioles." The part of plants 

 which springs upwards from the earth is called the stem, 

 if large the trunk, this divides into branches and twigs ; 

 stems in some cases continue for a distance more or less 

 underground. The part of a potato plant, usually called 

 the root, and from which the tubers or potatoes grow, is in 

 reality an underground stem, and the fibres which spring 

 from it are the roots ; the underground suckers of mint are 

 also portions of stem, and in some cases these are greatly 

 expanded, they then obtain the names of " tubers " (as the 

 potato), or " corm," as in the crocus and meadow saffron ; 

 when the stem is thin and runs along the ground, sending 

 in roots at intervals (as in the strawberry), it is called a 

 " runner," when thicker and running horizontally under the 

 ground, it is called a " rhizome." 



The stem consists of a, central portion, either made 

 up of long bundles of woody fibre running side by side, as 

 in the endogenae, or deposited in rings and having a central 

 cylinder of pith, as in the exogenae. In these the wood at 

 the central part (or the oldest) is called " duramen," or 

 " heart- wood," while that at the outer part or nearest to the 

 bark (the newest), is called "alburnum" or "sap-wood." 

 The former is the harder and the latter the softer portion. 



