Page:The Works of Aristotle - Vol. 6 - Opuscula (1913).djvu/116

828$a$ a third assimilation. In animals there is a third process of assimilation; this is due simply to the diversity of their limbs and to the distinctness of their parts from one another. Plants, on the other hand, are more homogeneous and repeat the same members over and over again, and the nutritive material generally has a downward tendency. The shapes of plants will depend on the character of the seed, while the flower and fruit is dependent on the water and nutritive material. In all animals the first process of maturation and concoction of the nutritive liquids takes place within the animal; there is no exception to this rule. But in plants the first concoction and maturation takes place in the nutritive material. Every tree continues to grow up, until its growth is completed and it dies. The reason is that, while in any animal its height is much the same as its width, in a plant it is far from being so, because water and fire, the elements which compose it, rise quickly, and therefore the plant grows. Variety in the branches of a plant is due to excessive rarity, and, when the moisture is intercepted there, the process of nature will cause it to grow hot and will hasten the concoction, and thus boughs will form and leaves will appear, as we have already said.

shedding of leaves from trees will be due to the tendency to fall, induced by quickly formed rarity. When the moisture is assimilated with the nutritive material, it will assume a pyramidal form, and therefore the ducts within will be wide and will afterwards become narrow; when the nutritive material makes its appearance already assimilated and formed, it will close up the extremities of the ducts above, and the leaves will have no nutritive material, and therefore dry up. When the contrary process