YfiGETATIVE OKGANS OF PLAXTS. 371 



the remaining parts being in moist air. Olilerts like- 

 wise proved that these plants flourish when only the 

 middle part of their roots is immersed in water. Keep- 

 ing the root-tips, the so-called spongioles, in the air, or 

 cuttiag them away altogether, was without apparent 

 effect on the freshness and vigor of the plants. The 

 absorbing surface Tyould thus appear to be confined to 

 those portions of the root upon which the development 

 of root-hairs is noticed. 



The absorbent force is manifested by the active root- 

 lets, and most vigorously vphen these are in the state of 

 most rapid development. For this reason we find, in 

 case of the vine, for example, that during the autumn, 

 when the plant is entering upon a period of repose from 

 growth, the absorbent power is trifling. Sometimes 

 water is absorbed at the roots so forcibly as not only to 

 distend the plant to the utmost, but to cause the sap of 

 th^ plant to exude in drops upon the foliage. This may 

 be noticed upon newly-sprouted maize, or 6ther cereal 

 plants, where the water escapes from the leaves at their 

 extreme tips, especially when the germination has pro- 

 ceeded under the most favorable conditions for rapid 

 development. 



The bleeding of the vine, when severed in the spring- 

 time, the abundant flow of sap from the sugar-maple 

 and the water-elm, are striking illustrations of this 

 imbibition of water from the soil by the roots. These 

 examples are, indeed, exceptional in degree, but not in 

 kind. Hofmeister has- shown that the bleeding of a sev- 

 ered stump is a general fact, and occurs with all plants 

 when the roots are active, when the soil can supply them 

 abundantly with water, and when the tissues above the 

 absorbent parts are full of this Kquid. When it is other- 

 wise, water may be absorbed from the gauge into the 

 stem and large roots, until the conditions of activity are 

 renewed. 



