Page:Popular Science Monthly Volume 27.djvu/811

Rh yet formulated by the botanist; again, when the winters are mild and the soil deep, it often shoots up rapidly, only to be snapped asunder by winds of moderate strength. Eucalyptus plantations, moreover, are very costly. If the ground is watery, it has to be drained, otherwise the roots rot; if the ground is heavy, trenches must be dug in it to make room for the long roots of the trees, and often these trenches have to be drained, as is done in the case of olives, in order to prevent the filtration water from stagnating and the roots from rotting. Hydraulic amelioration must have recourse to means less uncertain; and should the conditions of any locality counsel a trial of an absorbent plantation, it should be done with trees of our own hemisphere. The expense is smaller, and the trees are sure not to die.

At best, hydraulic amelioration is never certain, because the slight humidity of the soil necessary to develop malaria may easily be restored to it, even during the warm season. Combination of atmospheric with hydraulic amelioration has therefore been tried: to withdraw, that is to say, the humidity from the soil, while at the same time preventing the direct contact of the air with its malarious strata. Leaving the soil with layers of sound earth spread over it either alluvially or by the hand of man, and also draining the soil itself, was last year, at the instance of Dr. Tommasi-Crudeli, practiced on the grounds of the Janiculan Hill, near the Palazzo Salviati, in the Lungara. The entire area, having been thoroughly well drained and then covered with a dense coating of meadow soil in all those places which could not be paved with street rubble, has since remained without a single case of fever in the numerous personnel of the Military College occupying the Palazzo Salviati, while in the Palazzo Corsini, on the same side of the Lungara, but looking on the grounds of the Janiculan which are still exposed to the air and sun, there have within the same period been not a few cases of fever, some of them fatal.



AVING pointed out in a previous essay the lines of descent of vertebrata which have been brought to light by paleontological investigation, I propose to produce in the present article some evidence as to the nature of the forces which have been actively at work in effecting those changes of structure which constitute the evolution of one type of animal from another. We can obtain this evidence by comparing the successive steps of each line with one another. We thus learn the nature of the modifications, and can, as the case may be,