Miscellaneous, 



424 



of water in any given portion of soil, it is of course obvious that the root 

 should be branched out as much as possible, in order to get into as much of 

 the soil as it can, and in fact this is what we generally find. 



The simplest type of root is a primary root going straight down into the 

 soil (a taproot), and giving off side branches (PI. 1). An easy way of investigating 

 roots of this— or other— kind is to germinate seeds in a tumblerful of wet sawdust. 

 Take for example a gourd or pumpkin seed (PI. 1); the figure shows it with 

 one side of the seed coat removed, so as to exhibit the veining of one of the seed 

 leaves. If such a seed be carefully dissected (it is best to soak it in water 

 for 24 hours first), and the seed coat removed, it will be found to show two 

 " seed leaves" attached below to the top of a very small rootlet, while between 

 the seed leaves is a very small beginning of a shoot. 



Soak another seed in water for 24 hours, and put it in the wet (not 

 dripping, but simply wet) sawdust, with the narrow end of the seed close to 

 the glass. In a few days it will sprout, and a root will come out of the narrow 

 end, bend downwards, and grow. Examination of the now split seed will show 

 that the root has developed a little peg on one side, which holds the seed open 

 for the escape of the young plant. As the root grows downwards it will develope 

 lateral roots, and careful examination of these will show that they are developed 

 in a definite number of rows, each one that emerges from the main root being 

 in a direct line under some other one. 



The root emerges horizontally, or nearly so, but turns downwards at 

 once. This is not a mere accident, but is inherent in the nature of an ordinary 

 root. The shoot at the same time, emerging from the same seed, bends upwards. 

 When the root has grown for a few inches, tilt up the glass, and put a stone 

 under it to keep it in the new position, and leave it for a few days. It will 

 be seen that the root changes its direction of growth, and once more comes 

 into the vertical downward line, though the older part retains the direction in 

 which it first grew. Not only does the direction of the tap root change, but 

 also that of the lateral roots, as is roughly indicated in the figure (PI. 1). 



If the soil is uniformly wet, the main root will grow straight down- 

 wards, but if the soil be wet on one side and dry on the other, it will grow 

 towards the wet side, the greater degree of moisture on that side exerting a 

 greater effect upon it than does gravity. This may often be seen by growing a bean 

 or gourd seed in a glass of wet sawdust, the sawdust being kept wet on one 

 side only, when it will be seen that the root curves towards that side. 



The root does not absorb water, in most cases, directly through its 

 " skin," but by means of root-hairs. These may be seen in germinating mustard- 

 seeds (grow them on wet flannel) coming off from the stout roots as a dense felt of 

 fine hairs. It can be experimentally proved that it is only these that absorb water, 

 and as they are only near the tips of the roots, that only these are absorbent. 



While the principal function of the root is perhaps to absorb water, it 

 also has a very important function in the anchorage of the plant. It is obvious 

 that this will be subserved equally well by the branching and spreading out 

 of the root which serves for the purposes of absorption. A feature which very 

 much helps the performance of both these functions is the fact that the lateral 

 roots do not grow vertically downwards, like the tap root, but at a definite 

 angle with the latter, and keep to this angle, as their change of direction when 

 the glass is tilted shows. 



In a large number of plants we do not get a proper tap root at all, but 

 roots branch out from the base of the plant, and are then technically known 

 as fibrous roots (PI. 1). These may be specially easily and well seen in grasses, 



