CH. IV. EECOVEEY OF VEGETATION. 83 



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 main- 

 taining 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 \egetation, and thus compen- 

 sates for the destruction effected at an earlier fit age. It is 

 when the swarms appear late, and attack the wheat or 

 maize after the flowers are developed, that the conse- 

 quences to the population are very serious, and famines 

 result that periodically affect large districts. 



In the present year it was clear that rain had fallen 

 since the locust invasion, and although much damage had 

 been done, tolerable specimens of many plants here seen 

 for the first time were to be found. A few of these are 

 common to the Canary Islands and this part of Africa ; 

 others are not yet known except on this coast. The most 

 curious of them is the Seneoio (Kleinia) pteroneura, whot e 

 succulent almost leafless branches, as thick as a man's 

 finger, bear a few heads of flowers that differ little, save 

 in their larger size, from those of the common groundsel. 



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