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carbonate of lime. Usually they go on growing at the apical end, 

 while the lower parts embedded in lime die off. In consequence 

 the bed of the stream itself becomes calcified and elevated, and 

 in course of time banks of calcareous tufa are formed which may 

 attain to considerable dimensions. Banks raised in this manner 

 are known which are no less than 60 feet in height. To construct 

 them, mosses and other plants must have worked for more than 

 two thousand years. 



Numerous stone-worts (Chara and Nitella), the water-milfoil 

 and hornwort, water-crowfoots (Ranunculus), and more especially 

 pond-weeds, which grow in continuous masses in still inland 

 waters, incrust their delicate stems and leaves with lime during 

 the summer, but in autumn shrink aw r ay without leaving any trace 

 of the mass of vegetation until the following spring. The cal- 

 careous deposits, however, are preserved, and, sinking to the 

 bottom of the water, form a layer which year by year increases in 

 thickness. Anyone who investigates the wastes of water in the 

 shallow lakes of lowland districts will be convinced of the magni- 

 tude of the scale on which this kind of accumulation must take 

 place. 



As a boat glides over places where there is a luxuriant growth 

 of lime-encrusted chara and horn-wort there is a creaking sound 

 in the water like the snapping of dry sticks of birch wood. Great 

 numbers of stone-worts are fractured by the boat as it strikes 

 against them, and if one takes hold of the fragments they feel 

 like a heap of brittle glass. Similarly amongst the pond-weeds 

 (Potamogeton lucens) in particular the lime clothes its large 

 shining leaves with a very stout uniform crust, which drops off in 

 scales as the plant dries, the weight of which can be exactly 

 determined in the case of each separate leaf. There is no doubt 

 that in times past large lacustrine deposits of lime have been thus 

 formed. The spore fruits of stone-worts and the nutlets of pond 

 weeds found in them clearly show this. 



Absorption Glands with Incrustations of Lime. 



We have seen that the lime excreted on the leaves of certain 

 hydrophytes or water plants falls away and accumulates at the 

 bottom of lakes and streams. On the other hand, the lime is 

 sometimes employed in protecting the pores or stomata and 

 guarding against the too rapid evaporation of moisture. It is 

 also associated with what are known as absorption glands on the 

 leaves of certain plants exposed to dry conditions. Before dis- 

 cussing these I would first of all refer to water-collecting and 

 absorbing structures generally. In the case of the teasel there 

 are water receptacles which receive and hold water for weeks 

 together. In such water there are found the remains of decayed 

 earwigs, beetles and spiders, so that in such cases it is possible 

 that the water, and some organic compounds dissolved in it, is 

 susceptible of being taken up not only from the soil, but also by 

 means of absorptive appliances on the stem and leaves. Again, 



