105 



foraminifera for a repetition of shell building and, sinking- to the 

 floor of the ocean may rise again as towering majestic cliffs such as 

 are our Island's pride. 



IV. 



Lime as an Agent in the Nutrition, Protection and 

 Distribution of Plants. 



By Sir Daniel Morris, K.C.M.G., M.A., D.Sc, D.C.L. 



(Read before the Botanical Section, March 25th, 1915.) 



ANE of the commonest forms of lime is the carbonate of lime 

 " formed by the combination of the oxides of calcium and 

 carbon. This constitutes the bulk of the chalk deposits and the 

 mountain limestones. It forms, also, more than one-half of the 

 magne/sian limestones, and is present in varying quantities in 

 calcareous sandstones (sand and lime), and in marls (lime and 

 clay). Probably the majority of limestones are of organic forma- 

 tion ; that is, they consist of the debris of the skeletons of a vast 

 series of animals. Some of these animals, as in the case of the 

 Rhizopods or foraminifera, that have made up the large masses of 

 chalk, are very minute — in fact microscopic. Others, such as 

 crinoids or star fish, and shell-fish, such as oysters, clams and 

 molluscs generally are moderately large. Coral limestones are 

 being formed at the present day over a large extent of the 

 tropical seas, while globigerina ooze, which is continually accumu- 

 lating in the abysmal depths of oceans, and will eventually become 

 chalk, is the most widespread of modern calcareous formations. 

 As will be shown presently, there are quite appreciable deposits 

 of limestones that are entirely due to the action of plants. 



Among limestones we may distinguish chalk as the earthy 

 form, mountain limestone as the compact form, and marble as the 

 crystalline form. The purest of all natural varieties of the sub- 

 stance which is the basis of all limestones are the beautiful 

 crystals known as Calc-spar and Iceland-spar. 



Carbonate of lime is easily dissolved in rain water in the 

 presence of carbonic acid. When lime is present in water in 

 quantity it causes temporary hardness. When such water is 

 boiled, and the carbon dioxide driven off in bubbles, the lime is 

 deposited in the form of ''fur" in kettles and boilers; or when 

 dripping from the roof of caves the deposits known as stalactites 

 and stalagmites are formed. 



As is well-known, when ordinary limestone or chalk is heated 

 or burnt in a kiln, and the carbonic acid is driven off, we obtain 

 commercial quicklime. This may be regarded as almost pure 

 oxide of calcium. Usually when we speak of lime it is this oxide 



