VEGETATIVE ORGANS OF PLAKTS. 279 



The older parts of the roots, whieh are destitute of fifcrils 

 and which have nearly ceased to be active in the work of 

 absorption, are not affected by the change of circum- 

 stance. These facts, which are due to the researches of 

 Dr. Sachs {Vs. Si., II, p. 13), would naturally lead to 

 the conclusion that the absorbent surface of the root un- 

 dergoes some structural change, or produces new roots 

 with modified characters, in order to adapt itself to the 

 medium in which it is placed. It would appear thab 

 when this adaptation proceeds rapidly the plant is not 

 permanently retarded in its growth by a gradual change 

 in the character of the .medium which surrounds its 

 roots, as may happen in case of rice and marsh-plants, 

 when the saturated soil in which they may be situated at 

 one time is slowly dried. Sudden changes of medium 

 about the roots of plants slow to adapt themselves would 

 be fatalto their existence. 



Nobbe has, however, carefully compared the roots of 

 buckwheat, as developed in the soil, with those emitted 

 in water, without being able to observe any structural 

 differences. The facts above detailed admit of partial, if 

 not complete, explanation, without recourse to the suppo- 

 sition that soil- and water-roots are essentially diverse in 

 nature. When a plant which is rooted in the soil is 

 taken up so that the fibrils are not broken or injured, 

 and set into water, it does not suffer any hindrance in 

 growth, as Sachs found by his later experiments. (Ex- 

 perimental PJiysiologie, p. 177.) Ordinarily, the suspen- 

 sion of growth and decay of fibrils and rootlets is due, 

 doubtless, to the mechanical injury they suffer in remov- 

 ing from the soil. Again, when a plant that has been 

 reared in water is planted in earth, similar injury occurs 

 in packing the soil about the roots, and moreover the 

 fibrils cannot be brought into that close contact with the 

 soil which is necessary for them to supply the foliage 

 with water ; hence the plant wilts, and may easily perish 



