OBSERVATIONS UPON THE PHENOMENA OF PLANT-LIFE. 303 



water, nitrogenous matter, and such soluble minerals as eacli species requires 

 for its use. For this purpose it is admirably adapted by its peculiar structure, 

 substance, and mode of increase. The older portion of roots serves to sustain 

 the stem and hold it in place, and also acts as a reservoir of supplies to the 

 plant. The younger roots usually branch off in an irregular manner, and elon- 

 gate by the multiplication of cells near their extremities. The tips of roots are 

 usually very minute fibres of exceedingly delicate tissue, which insinuate them- 

 selves into the pores of the soil, and then, by the expansive power of growth, 

 enlarge these capillary channels to any required size. 



ROOTS 



of ordinary plants grow most freely in a loose, well-drained soil, containing the 

 essential elements of plant-food in a soluble form. They absorb their water 

 from the surface of the molecules of the soil, to which they attach themselves 

 by very minute, cellular papilla?, called root-hairs. These hairs are much more 

 numerous in a soil moderately dry than in one which is wet and heavy. The 

 most vigorous plants have the largest number and greatest extent of roots. 

 Hence the importance of deep and thorough tillage in preparing the ground 

 for crops. The growth of a plant depends chiefly upon the amount of water 

 which is exhaled by its leaves, and this necessarily depends upon the supply 

 furnished by the roots. The folly of ploughing between rows of corn, or other 

 plants, after their roots have spread widely through the soil, is self-evident. 

 Prof. L. B. Arnold says he has known the maturing of a corn-crop postponed 

 ten days by ploughing it at the last hoeing. 



THE PEXETRATIXG POWER AXD TEXDEXCY OF ROOTS 



is well illustrated in the case of an apple-tree on the College Farm, which 

 forced its roots down through a mass of coarse gravel eight feet, to obtain a 

 supply of water. The stones were about the size of hens' eggs, and so closely 

 packed by the waters of the drift period which deposited them, that the cylin- 

 drical form of the roots was entirely destroyed. The growing tissues pressed 

 themselves into every crevice so as actually to surround and enclose the ad- 

 joining pebbles. A similar root of an elm was recently dug up in Westfield, 

 Mass., and presented to the College Museum by Mr. B. H. Averell. Prof. 

 Stockbridge, last fall, washed out a root of common clover, one year old, grow- 

 ing in the alluvial soil near the Connecticut River, and found that it descended 

 perpendicularly to the depth of eight feet. Mr. Mechi, of Tiptree Hall, Eng- 

 land, tells us that the reason clover is usually so short-lived, is the fact that 

 the lower roots are either unable to penetrate the subsoil or to find in it the 

 requisite supplies of food. He also states that his neighbor, Mr. Dixon, of 

 Riven Hall, dug a parsnip which measured thirteen feet six inches in length, 

 but, unfortunately, was broken at that depth. 



The roots of lucerne often penetrate to the depth of more than twenty feet, 

 while the tap-roots of trees, continuing to grow for a long period, descend still 

 further. A British ofiBcer in India reports that the root of a leguminous tree — 

 the Prosopis spicigera — is often dug for economical purposes, and that he has 

 seer an excavation sixty-nine feet deep maile for such a root without reaching 

 its lower extremity. The roots of trees are well known to extend in a horizon- 

 tal direction to surprising distances, and to exert a very deleterious influence 

 on crops in their vicinity. The living roots of an elm, in Amherst, were found 

 in abundance at a distance of seventy-five feet from the trunk, which was just 



