744 PHYSIOLOGY. 



float it in the water; 2. To absorb liquid food ; 3, According to 

 some atithors, to excrete into the soil certain matters which are 

 injurious, or at least not necessary for the healthy development 

 of the plant ; 4. To act as a reserA^oir of nutriment. 



The office which the root performs, of fixing plants in those 

 situations where food can be obtained, is evident, and needs no 

 further remarks. It is also essential to the proper performance 

 of its absorptive powers. 



Absorption by the Root. — The function which the root performs 

 of absorbing nutriment for the uses of the plant, from the ma- 

 terials in or upon which it grows, is not possessed by its whole 

 surface, but is almost exclusively confined to the cells and fibrils 

 {fig. 224) of the newly developed portions and young parts 

 adjacent to them. As already mentioned, the dense cells at the 

 apex of the rootlets are not adapted for absorption. Hence, in 

 the process of transplanting, it is necessary to preserve such 

 parts as far as possible, otherwise the plants thus operated upon 

 will languish or die, according to the amount of injury they have 

 sustained. The injury done to plants in transplanting is also to a 

 great extent influenced by atmospheric circumstances and condi- 

 tions of the soil at the time in which such an operation is per- 

 formed ; thus, under the favourable circumstances of a warm soil 

 and moist atmosphere the destruction of a large portion of the 

 young extremities of the root will do but little injury, as the plant 

 will then speedily form new absorbent extremities ; but if the 

 conditions of the earth and soil be the reverse, then a large 

 destruction of the young extremities of the roots will cause the 

 plant to die before new absorl:)ent extremities can be formed. 

 •Special attention should be paid to the above facts when trans- 

 planting is performed in the growing season ; but it is far better, 

 when possible, to transplant late in the summer or in the autumn 

 when the growing season is drawing to a close, or in the spring 

 before it has recommenced, as at such periods little or no ab- 

 sorption takes place, and the plants have accordingly time to 

 recover themselves, before they are required to perform any 

 active functions. (See p. 796.) 



This absorption of food by the youngest rootlets is due to os- 

 mose taking place between the contents of their cells and the 

 fluids of the surrounding soil. 



Roots, as we have already seen (page 112), only grow in 

 length by additions near to their extremities, and as it is at 

 these parts that absorption of food almost entirely takes place, 

 they are always placed in the most favourable circumstances for 

 obtaining it, because in their growth they are constantly entering 

 new soil, and hence, as one portion of that soil has its nutritious 

 matters extracted, another is entered which is in an unexhausted 

 state. It has also been shown, by direct experiment, that when 

 the roots meet with a store of nourishment in the soil, a gi'eatly 



