468 POPULAR BOTANY. 
While these three plants indicate the presence of zinc, other kinds in 
return point to the layers of lead, copper, iron, coal, lime, chalk, gypsum, 
marl, &c. 
A very interesting demonstration in regard to the abilities of plants 
to accommodate themselves to conditions of locality, presents itself to the 
naturalist in swamps which are occasionally inundated, particularly if 
the water on some places is kept running for some time. For instance, 
plants grown in swamps, and constructed to live in the open air, would 
certainly be drowned, when set under water for a long time, if they were 
not provided with the means to rescue themselves from such a dilemma. 
Under this difficulty, full grown plants begin once more to grow, not 
seldom to a great extent until they have reached the surface of the water, 
where the leaves lay down ; while the stem takes up again its ordinary 
functions. On places, however, where the water is running, the plants 
or their parts will appear in entirely different forms — namely, by the 
continual side pressure of the water the new growth will be unnaturally 
extended, or, as if it were pulled into the shape of long slender threads, 
and the foliage will undergo a similar change, whose flat forms were 
altered into long thin splits. In case such an extended stem should 
reach a place where the water stands still, the leaves will appear again 
in their original large shape. When the water on such inundated places 
runs off or is evaporated, the plants become so tender that they cannot 
live in the open air any more. The whole growth therefore, must decay 
as deep as to the roots, and the new plants which shall spring up from 
them appear also in their original form again. 
These and other similar changes in the forms of plants bring young 
botanists often into great confusion, and have also given rise to many 
discussions and different opinions among the experienced. 
I can hardly let this occasion pass without referring to the peculiar 
organisation of a plant which grows frequently in our ponds — namely, 
the Utricularia vulgaris, or bladder-weed. The stem of this plant is so 
herbaceous and weak that it cannot bear its own weight, and is there- 
fore constantly submerged. These plants, however, belong to the an- 
nuals which, must bear seed every year in order to reproduce 
themselves anew ; but as the production of seeds cannot take place 
under water, and as the stem is notable to rise above the surface, Nature 
has found an ingenious plan. The setaceous leaves have been provided 
with a great number of small bladders filled with light gas, and by 
means of these buoys, the flower-stalks are raised to the surface, where 
the fructification takes place, and after the seeds have grown to maturity 
they drop to the bottom of the water, from which they spring up again 
at the following season. 
Having now paid some attention to those plants which are accustomed 
to grow in soil and water, we will now turn to the parasites — such plants 
namely, as are in the habit of growing on trees, or stones and rocks, &c. 
