IRISH GARDENING 



73 



Roots and their Functions. 



By G. O. Sherrari). 



IN dealing with plant life it is very necessary 

 to have a clear conception of the structure 

 and function of the plant body as a whole, 

 and of its members in particular, if the principles 

 governing good cultivation are to be rightly 

 understood. It is proposed in the course of this 

 article to briefly discuss the functions of roots 

 and the structural adaptations which enable 

 them to perform those functions efficiently, also 

 the soil condi- 

 tions most suit- - — -<=^.-* « 

 able for healthy ^. ftyy^K-lft^i^^^^'^r^:^ 

 root action. 



The two most 

 obvious uses oi' 

 the root are to 

 fix the plar.t in 

 the soil and to 

 supply it with 

 n o u r is h m e n t 

 therefrom, al- 

 though the exact 

 kind of nourish- 

 ment supplied 

 by the root is by 

 no means so ob- 

 vious, and was 

 the subject of a 

 prolonged c o n- 

 troversy between 

 two very cele- 

 brated agricul- 

 tural chemists — the nitrogen 

 third and very common root 

 of food storage. We see 



ibsorbing reg 



Showing growing tip 



controversy. A 

 function is that 

 it well exhibited 

 in the case of the thick roots of the dock 

 or dandelion or the swollen tap-root of the 

 parsnip ; in reality, the great majority of per- 

 ennial plants store reserve food in their roots. 

 Anchorage of the plant is secured either by a 

 deeply-penetrating tap-root (as in the oak) or a 

 widely-spreading network oi' surface roots (as 

 in the beech or Scots pine). In most trees the 

 root system extends over an area at least equal 

 to the spread of the branches, giving the tree a 

 wide and firm purchase in the soil. In the case 

 of trees, the older portions of the root become 

 woody, while the roots of herbs are either 

 fibrous (like those of grasses) or fleshy (like the 

 parsnip or carrot.) 



It is necessary, both for purposes of anchor- 

 age and food absorption, that the root should 

 be able to readily penetrate the soil and travel 

 through it without injury. The elongation of 

 the root takes place at a region close behind the 

 extreme tip. At the tip itself the cells com- 

 posing the root divide arid multiply. Immedi- 

 ately behind the tip the newly-formed cells 

 elongate, so that the root tip itself is pushed 

 forward into the soil. In order that the root 

 should penetrate the soil without injury, the tip 

 is covered by a protecting cap of cells, which, as 

 as fast as they 

 are rubbed off 

 through friction 

 with the soil, are 

 reinforced from 

 behind by cells 

 formed at the 

 outside of the 

 growing region, 

 or growing point, 

 as it is called 

 This growing 

 point of the root 

 is sensitive to 

 certain influences 

 and behaves like 

 the nervous 

 centre of an ani- 

 mal, transmitting 

 impulses to the 

 cells behind it. 

 Thus the grow- 

 ing point of a 

 main root is sensitive to the action of gravity, 

 and always tends to grow vertically downwards 

 It does not matter if a seed lies in the soil in 

 such a position that the root on emergence 

 points upwards — it will at once begin to bend 

 round and grow downwards, while the shoot 

 will turn in the opposite direction and grow 

 upwards. If a germinating seed were caused 

 to rotate in a vertical circle so that the force 

 of gravity would act on all sides of the growing 

 root in turn, and thus neutralise itself, it would 

 be found that the main root would grow out 

 horizontally. Side roots are not affected b\ 

 gravity in the same way, but tend to grow out 

 in a horizontal or oblique direction. Other 

 stimuli which have an action on roots are light, 

 contact, and moisture. All roots tend to turn 

 away from light, as may readily be seen by 



