DEFINITION OF THE ROOT. 765 



into the configuration of plants, it is a matter of great import how the definitions 

 of the individual parts and members of the plant are formulated, and whether the 

 author lays particular stress on this or that characteristic. Suppose that some 

 observer holds the opinion that the presence or absence of the root-cap afiurd.s an 

 important distinction between a root and stem; then he would speak of the supports 

 of mangrove-trunks as lateral stems which grow downwards; another, who lays 

 particular weight on the fact that roots produce no leaves behind their gi'owing 

 points, would, on the contrary, declare the supports of the mangrove-ti-unk to be 

 roots devoid of root-caps. It would be the same with the contradictory explana- 

 tions and different appellations which would be given to the supports of Clusiaceae 

 and figs, to the fixing and absorbent apparatus of Mistletoe which penetrate into 

 the host-plant, and to so many other hypogeal and epigeal parts of the plant-body. 



These examples will suffice to show how a conflict may arise over such an appa- 

 rently simple thing, how easily the investigators into the region of the speculative 

 science of form may become one-sided, what great difl&culties are to be encountered 

 in formulating a definition, and how in particular a hasty generalization must be 

 avoided about characteristics which it is not at all certain are really to be met with 

 universally. Every definition is dependent upon the extent of our knowledge at 

 the time; it may not hold good as our experience widens, and therefore has only 

 a relative value. 



From the standpoint of our present knowledge, however, the following may be 

 taken relatively as the best definition: — A root is a body of tissue provided with 

 vascular bundles, which originates from an older, previously-existing part of the 

 plant; its growth is not limited, and it never directly gives rise to leaves. 



In connection with this definition, some remarks may be made here by which 

 many relations between the root and other parts of the plant will be elucidated. 

 First it should be noted that in the above definition the youngest developmental 

 stage, viz. the embryo, is included under the term " plant". It has further to be 

 explained why the characteristic which is first thought of in non-botanical circles, 

 when speaking of roots, viz. their power of deriving fluid nourishment from 

 another body, has not been mentioned in the above definition. It is perfectly correct 

 to say that an absorption of fluids is generally observed in roots, but in reality it 

 is only the root-hairs proceeding from the roots w^hich perform this task, and these 

 absorbent cells are known to be also developed on stems and leaves. The coty- 

 ledon extended from the seed of the Bulrush (Typha), penetrates into the soil with 

 absorbent cells. The cavities of the green leaf-structures in insectivorous plants 

 are also abundantly provided with them, and special absorbent cells are developed 

 on the green leaves of many saxifrages, tamarisks, and so forth; whilst in those 

 marsh-plants, the leaves of which float partly on the surface of the water and are 

 partly submerged, the epidermal cells also function as absorbent cells. In many 

 aquatic plants (e.g. Hottonia, Ceratophyllum, Ahiias) absoq tion is only carried on 

 by means of the epidermal cells of the foliage-leaves, and no trace of roots is to 

 be found in them. Their foliage-leaves, however, remind one very much of root- 



