'246 



SCIENCE OF AGRICULTURE. 



Part II. 



1593. The descending root, an anomaly which attends some perennials, is at first spindle-shaped and per- 

 pendicular, sending out some lateral fibres, but dies at the lower extremity in the course of the succeed, 

 ing winter, and protrudes new fibres from the remaining portion, and even from the lower portion of the 

 stem, in the course' of the following spring, which, by descending into the soil, draw down the plant with 

 them, so that part of what was formerly stem is now converted into root. This process is repeated every 

 year, and by consequence a portion of the stem is made to descend every year into the earth. The 

 anomaly may be exemplified in the roots of Faleridna dioica, Tanacfetum vulgire, and O'xalis Acetos^Ua ; 

 and will also account for the bitten and truncated appearance of Scabiijsa succlsa, or devil's bit. 



1594. Migratory roots depend on a principle similar to the foregoing. If the stem of a descending root 

 happens to be creeping or procumbent instead of being erect, then the lateral shoots from above are carried 

 forward in the direction of that procumbency, so that in the course of a few years the plant has actually 

 changed its place by so much as the stem has been converted into a root. This is well exemplified in the 

 genus i^ris, a plant of which, as it enlarges in circumference, dies in the centre, and presents a ring of 

 plants instead of a solitary one. In the case of some aquatics, which float about on the surface of the 

 water as they happen to be driven by the winds, the whole plant may be said to be migratory, as in the 

 genus L^mna, and some marine plants. 



1595. The beet-root, if dissected when about a year old, presents the singular anomaly of being already 

 furnished with from five to eight distinct and concentric circles of longitudinal tubes or sap- vessels, im- 

 bedded at regular intervals in its pulp; whereas other biennial roots form only an individual circle each 

 year, and are, consequently, at no time furnished with more than two. 



1596. Roots changed to branches and branches to roots. If the stem of a young plum or cherry tree, but 

 particularly of a willow, is talien in the autumn, and bent so as that one half of the top may be laid in the 

 earth, one half of the root being at the same time taken carefully out, but sheltered at first from the cold 

 and then gradually exposed to it, and the remaining part of the top and root subjected to the same process 

 in the following year, the branches of the top will become roots, and the ramifications of the root will 

 become branches, protruding leaves, flowers, and fruit in due season. 



1597. The stem. If the stem of a tree planted by a pond or river is so bent in its 

 growth as to come near to the surface of the water and to be occasionally immersed in it, 

 it will sometimes send out from the under surface a multitude of shoots that will descend 

 into the water, and develope themselves in the manner of the fox-tail root. Sometimes 

 it happens that a stem, instead of assuming the cylindrical form common to the species, 

 assumes a compressed and flattened form similar to the herbage of the Cactus, as in the 

 fir tribe, ash, &c. 



1598. The anomaly of the flattened stetn {fig. 190.) is accounted for by Du 

 Hamel, by supposing that an unnatural junction must have taken place in the 

 leaf-bud ; and so united shoots that would otherwise have been distinct. 

 Sometimes the stem is disfigured by accidental tumours or bunches projecting 

 from the surface, and forming ultimately what are called knots in the wood. 

 They are very common in the oal- and elm, and are produced, perhaps, by 

 means of some obstruction in '.c channel of the sap's motion, by which the 

 vessels become convoluted and ;.well up into a bunch. 



1599. But bunches are also to be met with on the stems of herbaceous plants, 

 as on that of the Carduus pratensis; of which you will often find a portion 

 near the top swollen out into an egg-shaped or egg-oblong bunch, extending 

 from an inch to two inches in length, and about an inch across. If this 

 bunch is cut open in the month of August, it will be found to contain several 

 large and white maggots. It has consequently been occasioned by the 

 puncture of the parent insect depositing its eggs. It does not seern to affect 

 the general health of a vigorous plant, though it might prove seriously in- 

 jurious to a weak one. 



160(). Bundled stem. Sometimes two or more contiguous stems, extending 

 in the process of their growth till they meet and press against one another, 

 become incorporated at length into one, and form a sort of bundle, lliis is 

 what may be termed a natural graft, in opposition to an artificial graft, of 

 which it is the model and prototype. The natural graft is always effected 

 by means of the union of the liber of the respective stems composing it ; so 

 that the perfection of the art of grafting consists in applying the liber of the 

 graft and stock together, in such a manner as shall most facilitate their; 

 in:;orporation. 



1601. The branch. If the branch of a tree is situated, as in the foregoing case of the 

 stem, so as to be partially or periodically immersed in water, it will send out also the 

 same sort of brush-like shoots. 



1602. Bunches or knots, exhibitinga plexus of young shoots {fig. 191. a) issuing from nearly the same i>oint, 



crossing in all directions, and finally incorporating together by means of a sort of natural graft, frequently 

 disfigure the branch. These bunches are frequently to be met with on the branches of the birch tree, and are 



