ANNUAL MEETING. 159 



As soon as the tip of tlie radiclo protrudes h-oni tlio soed-coats, it begins to 

 circumnntate, and the whole growing part continues to do so, probably as long 

 as growth continues. AV^hen the earth closely surrounds the roots they may, 

 perhaps, be quite prevented from circuninntating. Tlie tendency tocircutnnu- 

 tate must aid in finding tlie ])laces of least resistance in tlic soil. Geotropisni 

 does not give a root force sufficient to penetrate the ground, but merely tells 

 it which course to pursue. The strength of tlie radicle of a bean is notenough 

 to indentate the thinnest tin foil, when placed horizontally with the radicle 

 thrust ))erpcndicularly downwards. Tlie radicle in sucli cases turns to one 

 side and glides over tlie tin-foil without making any impression. The growing 

 part does not act like a nail driven into a board, but more like a wedge of 

 wood driven slowly into a crevice. 



I spoke of the firm root-tip and the spot just back of it where tlie cells 

 multiplied to extend the root in length. If this root-cap be killed with nitrate 

 of silver, not killing the spot where the cells multiply, the root ceases to act 

 as before, but wanders about in every direction, up, and off, and down, appar- 

 ently without any object in view. It acts wild or crazy. In three or four 

 days a new cap is produced, when geotropism again acts on them as before. 

 Darwin says, ''abundant evidence has been given, showing that with various 

 plants the tip of the radicle (root) is alone sensitive to geotropism, and that 

 when thus excited it causes the adjoining parts to bend." 



"There is no structure in plants more wonderful, as far as its functions are 

 concerned, than the tip of the radicle. The course pursued by the radicle in 

 penetrating the ground must be determined by the tip, hence it has acquired 

 such diverse kinds of sensitiveness. It is hardly an exaggeration to say that 

 the tip of the radicle (root) thus endowed, and having the power of directing 

 the movements of the adjoining parts, acts like the brain of one of the lower 

 animals, the brain being seated within the anterior end of the body, receiving 

 impressions from the sense organs, and directing the several movements." 



The old name of the root-cap was sjjongiole. It was formerly thought that 

 this was the most active part in absorbing nourishment for sustaining the 

 growth of the plant. Abundant evidence lias since been produced to show 

 that the tips of roots do not absorb much, if any, nourishment. They do not 

 "sponge" a living in any sense of the word. 



A little way back from the tip, along the sides of the young rootlets, the cell 

 walls are thinner and actively absorb water with what it holds in solution. In 

 case of our deciduous trees the young roots produce an immense multitude of 

 root hairs, tricliomes, resembling mould or spider webs. These hairs vary in 

 length and somewhat in shape, especially where they crowd between the par- 

 ticles of soil. This is here illustrated. These root hairs, so far as I know, 

 or have ever seen, each consists of an elongation of one of the outer cells of 

 the young plant. The root hairs vastly increase the surf ace of the roots, and 

 bring the plant into the closest relation to the soil. In warm weather, when 

 the plant is growing rapidly, the root hairs live only for a few days. They 

 rapidly perish, and their places are supplied by others. Root hairs are not pro- 

 duced except on young rootlets of the same season. 



I have examined and watched carefully at different times the young 

 stems of several kinds of vines. A hoi^ vino or grape vine twines or climbs to 

 the top of a straight stake or support. It reaches up some higher, perhaps 

 two or three feet; when it becomes no longer stout enough to rema;n in this 

 position it falls and takes a horizontal position, at right angles to the stake. 



