Mogador has long been tolerably well known to botanists. It was visited by Broussonet at the latter end of the last century, and was for some time the residence of Schousboë. More recently the neighbourhood has been explored by the late Mr. Lowe and by M. Balansa. We could not, therefore, reasonably expect to find here anything new to science; but our short excursion was nevertheless full of interest, though not altogether of an agreeable kind. We here saw for the first time a district recently ravaged by locusts; and while we acquired a lively sense of the amount of mischief effected by these destructive creatures, we also found out how it happens that the damage is confined within tolerable limits; how, in short, they fail to turn the country into a desert. When one reads the reports of credible eye-witnesses, who describe the arrival of swarms of locusts that devour every green thing, one asks oneself how it can be possible for man or animals to survive such destruction. In the first place, it may be remarked that, like most other sweeping statements, these are not strictly true. The locusts do not, in point of fact, devour every green thing. In the spots where they were most destructive we always remarked that certain plants escaped untouched. The result of this immunity would naturally be to substitute the latter for the species destroyed by the locusts, were there not some very efficient agency for repairing the damage and maintaining the life of the species, if not of the individual. An important element in considering this question is the season at which the mischief is effected. The young locust grows very fast, and it is mainly during the period of growth that it consumes vegetation. When once the animal has attained its full size, it becomes comparatively inert, and its capacity for destruction is vastly diminished. If the swarm of young locusts arrives before the middle of April, when the rainy season is not quite over, the first showers revive the plants that have been devoured almost to the root with surprising rapidity. Perennial species throw out new buds, and are soon again covered with leaf and flower; and the same often happens with annuals, unless these have already shed their seed, and then a new crop soon reappears. It may be supposed that the vast amount of decaying animal matter left on the surface, even in the most barren spot, contributes not a little to the vigour of the vegetation, and thus compensates for the destruction effected at an earlier stage. It is when the swarms appear late, and attack the wheat or maize after the flowers are developed, that the consequences to the population are very serious, and famines result that periodically affect large districts.