takes place, as we have said, the leaves do not fall from the trees. When coldness dominates in the plant, it will affect its colour owing to the secretion of heat in the middle of the plant and the presence of cold outside in its extremities; {{Right sidenote|828b the result is that the leaves are blue-grey and do not fall, as in the olive, and myrtle, and similar trees. When trees or plants exercise a violent force of attraction, fruit will be produced once a year; when they do not exercise such a force, nature will employ the process of concoction on successive occasions and at each concoction they produce fruit, and so some plants bear fruit several times in the year. Plants which are of the nature of water bear fruit with difficulty on account of the predominance of moisture in them, and the wideness of their ducts and the tendency of their roots to fall off; when the heat is intense, the assimilation will be quick and will be rarefied owing to the water and will not solidify; this we shall find to be the case in all small herbs and in some vegetables.
A grey colour will occur where the ground is exceedingly hot; here there will be little moisture and the ducts will become narrow, and when nature wishes to bring about assimilation it will not have sufficient moisture to supply the nutritive material and the ducts will become narrow. The process of assimilation therefore will be reversed and the heat will cause it to continue, and the plant will be seen to have a colour, intermediate between white and black. When this happens it will have black wood or anything approximating to white and ebony, that is, any of the whole range of colours from that of ebony to that of elm;[1] and so such wood sinks in water because its parts are compact and the ducts in it are narrow, and no air enters into them. When white wood sinks the reason will be the narrowness of the ducts and the presence of superfluous moisture, which blocks up the ducts so that the air does not enter; consequently it sinks. Every flower is composed only of rarefied material when the assimilation first begins; and so the flower generally precedes the fruit in plants. We have already shown why it is that plants produce their- ↑ Reading ulmum.
