ADVENTITIOUS ROOTS 29 



Although common upon monocotyledons adventitious roots 

 are not confined to this class. Examples are abundant upon 

 many kinds of dicotyledonous plants. Good instances are met 

 with on the underground stems of mint, potato (Fig. 144) and 

 hop, and on the runners of the strawberry, stems of creeping 

 crowfoot (Fig. 21) and white clover, as well as many others. 



They are generally produced at the joints where leaves grow 

 upon the stem, and may arise in some plants {e.g., on strawberry 

 runners) from internal causes apart from any external influences ; 

 in other instances their development depends upon contact of the 

 stem with water or moist soil. Almost all parts of certain plants 

 may be made to produce them, and, the propagation of plants 

 such as gooseberries, currants, roses and hops by means of slips 

 and cuttings depends upon their development. Pieces of stem 

 cut off just below a leaf, and placed in moist earth soon develop 

 adventitious roots near the cut end. Advantage is taken of their 

 formation in the propagation of plants by means of layers. 



Ex. 17. — Examine the roots on young strawberry runners in July. Also 

 those on creeping crowfoot, yoHnc; shoots of ivy, underground stems of 

 potato, couch-grass and mint, and on the lower parts of the stems close 

 to the ground, of oats, wheat, and barley. Note the position, number, and 

 extent of these roots. 



Examine the roots upon any cuttings or slips which can be obtained, and 

 observe whether they arise on the cut surface or at a point some distance 

 away from it. 



Usually adventitious roots are thin and fibrous, but those of 

 the dahlia are tuberous. 



6. The complete root-systems of plants vary enormously in 

 extent, but in all cases the total length is much greater than is 

 usually anticipated. That of an ordinary oat plant, although not 

 spreading through more than a cubic yard or two of soil, 

 measured in one instance over one hundred and fifty yards in 

 length. 



A tree uprooted by the wind exposes to view a small number of 



