122 ROOT. 



31. The latter office is essential to the certain and regular performance 

 of the former. 



32. It is not by the whole of their surface that roots absorb food ; but 

 only by their young and newly formed extremities, called Spongioles. 



33. Hence the preservation of the spongioles in an uninjured state is 

 essential to the removal of a plant from one place to another. 



34. A Spongiole consists of very young vascular tissue (12) surrounded 

 by very young cellular substance (5). 



35. It is therefore one of the most delicate parts of plants, and the most 

 easily injured. 



36. Hence whatever is known to produce any specific deleterious action 

 upon leaves or stems, such as certain gases (298) and mineral or vegetable 

 poisons, will produce a much more fatal effect upon the spongioles. 



37. These organs have no power of selecting their food, but will absorb 

 whatever the earth or air may contain, which is sufficiently fluid to pass 

 through the sides of their tissue. 



3S. So that if the spongioles are developed in a medium which is of an 

 unsuitable nature, as they will still continue to absorb, they cannot fail to 

 introduce matter which will prove either injurious or fatal to life, accord- 

 ing to its intensity. 



39. This may often explain why trees suddenly become unhealthy, with- 

 out any external apparent cause. 



40. Plants have the power of replacing spongioles by the formation of 

 new ones ; so that an individual is not destroyed by their loss. 



41. But this power depends upon the co-operation of the atmosphere, 

 and upon the special vital powers of the species. 



42. If the atmosphere is so humid as to hinder evaporation, spongioles 

 will have time to form anew ; but if the atmosphere is dry, the loss by 

 evaporation will be so much greater than can be supplied by the injured 

 roots, that the whole system will be emptied of fluid before the new spon- 

 gioles can form. 



43. This is the key to Transplantation (XV.) 



44. As roots are destitute of leaf-buds (IV.), and as leaf-buds are essen- 

 tial to the multiplication of an individual (10S), it should follow that roots 

 can never be employed for the purpose of multiplication. 



45. Nevertheless, roots when woody have, occasionally, the power of 

 generating adventitious leaf-buds (IV.) ; and when this is the case, they 

 may be employed for the purpose of multiplication ; as those of Cydonia 

 Japonica, &c. 



46. The cause of this power existing in some species, and not in others, 

 is unknown. 



47. It is therefore a power that can never be calculated upon, and whose 

 existence is only to be discovered by accident. 



48. Although roots are generated under ground, and sometimes at con- 

 siderable depths, yet access to a certain quantity of atmospheric air appears 

 indispensable to the healthy execution of their functions. This is con- 

 stantly exemplified in plants growing in the earth at the back of an ill- 

 ventilated forcing-house, where the roots have no means of finding their 

 way into the earth on the outside of the house. 



49. It is supposed by some that the introduction of oxygen into their 

 system is as indispensable to them as to animals. 



