THE ROOTS OF PLANTS 



91 



and the whole plant may be said to consist of two cones, attached by their bases. The 

 thicker part of the root is termed the cattdcx, the minute apex, the Jiirilla, and its 

 terminal point, the spongiola. Both of these parts, as has been proved by experi- 

 ments, have the power of elongating themselves, but more especially the part near to 

 the free extremity. Our readers may satisfy themselves of this fact by taking any fast- 

 growing root, as of a hyacinth growing in water, and tying a thread around the roots at 

 known intervals, and, after the lapse of a few weeks, ascertain, by admeasurement, the 

 total and relative elongation of the root and its parts. If a plant be selected, the root 

 of which grows in the ground, it will be found that the relative proportions of growth of 

 the upper, as contrasted with the lower portion, is infinitely less than in plants growing 

 in water. This is to enable the root to penetrate with less difficulty the resisting 

 medium. In this mode the roots of forest trees are enabled to penctra^ *he soil for 

 many yards from the base of the stem, so as to enable them to get the wnver and other 

 articles of food which may not be readily afforded at the base of the stem. 



The tissues of wh. jh the roots are composed are nearly the same with those of the 

 stem, viz., woody fibre, ducts, and cellular tissue. The woody fibre does not penetrate 

 into the spongioles, but is restricted to the parts immediately above it, whilst ducts and 

 cellular tissue are met with exclusively in those organs. The reason of this arrange- 

 ment is that the spongiole is an organ of absorption as well as of growth, and by it all 

 the fluids which enter the plant are introduced ; it is, therefore, not restricted to one 

 point, as the apex of the 

 root, but is found on various 

 parts of it (as may be seen 

 on the side of the radish), 

 wherever absorption can be 

 effected ; and it is of the 

 greatest importance, in 

 transplanting trees, to avoid 

 the destruction of too many 

 of these delicate thread-like 

 organs. Some writers re- 

 strict the term spongiole to 

 the very extremity of the 

 delicate fibrilla, which is 

 somewhat tumefied ; and 

 there it is said to consist 

 of a mass of small cells. 

 This is probably the true 

 statement of the case, as 

 may be seen by placing a 

 thin section of the end of a 

 root of the radish under 

 the microscope ; and then 

 we must regard the ducts 

 to which it leads as organs 

 destined to convey fluids 

 from the spongiole to the caudex of the root. The spongioles have also the power to emit 

 from the root effete and deleterious substances. Thus it is said that trees (as a pear 



Fig. 148. The PANDANVS, or SCREW PINK, emitting aerial root* 

 at a, b, e, d, and e, which ultimately reach the ground, and give 

 increased stability to the stem. 



