13 
It seems that titanium is inert toward plant growth. It is ex- 
tremely insoluble and occurs to some extent as small fragments of a 
black mineral, possibly ilmenite. Generally speaking, the titanium 
soils are silty, but sometimes they have a very fine texture. In a 
few places in the upper portion of the Wahiawa district, Opaeula 
and Kunia on Oahu, and near Pogue's station on Maui it occurs in the 
form of a blue gray layer composed of very fine particles which soil 
the fingers very much like charcoal. Sometimes a high percentage of 
ferrous iron is associated with the titanium. If phosphoric acid should 
become chemically combined with the titanium, the insoluble nature 
of this compound would render it unavailable to plants. 
CORAL SAND SOILS. 
These soils are of relatively small importance and are located near 
the sea level. Such soils, as the name indicates, have been formed 
mainly from grains of coral sand, which are composed chiefly of 
calcium carbonate. After the sand banks have been built up above 
sea level, organic matter and small amounts of soil gradually become 
incorporated with them, and certain plants soon gain a foothold, re- 
sulting in the formation of humus and later in a fairly fertile soil. 
An important use to which the coral beds and sand banks are being 
put is as a source of lime which is recommended for use where liming 
is needed. 
LIME-MAGNESIA RATIO. 
Hawaiian lava contains considerably more lime than magnesia, but 
frequently the opposite is the case with the soil. Generally speaking, 
the soils formed from black sand contain much higher percentages of 
magnesia than lime. Therefore, the lime-magnesia ratio is abnormal. 
So far as is now known, however, no injurious effects are produced on 
crops. Experiments carried out with the object of modifying the 
ratio of lime to magnesia have not indicated any practical advantage 
to be derived in this way. The lime is much more soluble than the 
magnesia, even where the magnesia content greatly exceeds that of 
lime. 
ACIDITY OF HAWAIIAN SOILS. 
Notwithstanding the highly basic character of Hawaiian soils, they 
generally give an acid reaction toward litmus. The acidity, as deter- 
mined by the Vietch method, sometimes indicates the need of large 
amounts of lime. In harmony with this is the very low content of 
carbonate except where coral sand is present. The soils around 
Honolulu, for example, contain not more than 0.1 per cent carbon 
dioxid (C0 2 ), although the lime and magnesia are high. It has been 
supposed that the sod lands are generally acid, but it seems that the 
slow growth of crops is- due more to the lack of aeration than the 
presence of actual acidity. Lime has been used to considerable 
