THE VEGETATIVE ORGANS OF TLAXTS. 249 



Bean (Phaseolas midtiflorus] 6 inches of mercury. 

 Nettle - 14 " " 



Vine - 29 " " 



Seat Of Absorptive Force, Dutrochet demonstrated 

 that this power resides in the surface of the young and 

 active roots. At least, he found that absorption was ex- 

 erted with as much force when the gauge was applied to 

 near the lower extremity of a root, as when attached in 

 the vicinity of the stem. In fact, when other conditions 

 are alike, the column of liquid sustained by the roots of a 

 plant is greater, the less the length of stem that remains 

 attached to them. The stem thus resists the rise of liquid 

 in the plant. 



While the seat of absorptive power in the root lies near 

 the extremities, it appears from the experiments of Ohlerts 

 that the extremities themselves are incapable of imbibing 

 water. In trials with young pea, flax, lupine, and horse- 

 radish plants with unb ranched roots, he found that they 

 withered speedily when the tips of the roots were immers- 

 ed for about one-fourth of an inch in water, the remaining 

 parts being in moist air. Ohlerts likewise proved that 

 these plants flourish when only the middle part of their 

 roots is immersed in water. Keeping the root-tips, the 

 so-called spongioles, in the air, or cutting them away alto- 

 gether, was without apparent effect on the freshness and 

 vigor of the plants. The absorbing surface would 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 rootlets, 

 and most vigorously when 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 ab- 

 sorbent power is trifling. The effect of this forcible en- 

 trance of water into the plant is oftentimes to cause the 

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