202 



of the apple, aurJ. the various species of scale-insects destructive 

 to citrus-fruits to establish this fact." 



This was written with reference to the United States, but 

 may be taken as applying with even greater force to tropical 

 countries, where the coccida; are apparently much more 

 abundant. The amount of damage done in any particular case 

 is not always easy to estimate, from various causes. Thus, in 

 the case of the cocoanut, it is probable that those who have 

 attributed the death of the palms to coccida; have over-estimated 

 the influence of these insects, since we now know from the re- 

 searches of Dr. Plaxton and Mr. Fawcett that the cocoanut is 

 subject to the attacks of fungous and bacterial parasites, and the 

 probability is, that the scale-insects in this instance only hasten the 

 end inevitable from other causes. On the other hand, I believe 

 the damage done is frequently under-estimated. When a tree 

 or shrub is dotted all over with scales, behind every one of 

 which is an insect living on the sap, the drain on the resources 

 of the plant must be considerable. In the case of small plants, 

 as for example a capsicum attacked by Diasjns lanatus (u. sp.), 

 death may speedily ensue : but trees as a rule survive the injury, 

 and finding that they continue to live and bear fruit, we are apt 

 not to reflect that they would do better if protected from the 

 attacks of insects. In order to ascertain accurately the influence 

 of insect pests on any kind of tree, it would be necessary to 

 fake several growing in the same locality, and carefully spray 

 some, while neglecting the others. If this were carried on for a 

 number of years, no doubt the difference to be observed would 

 be very marked ; and in the case of very seriously attacked 

 plants, it would be a difference between living and dead. 



It may be objected, that a drain on the vegetative tissues 

 of a tree is not necesssarily harmful ; as we are obliged fre- 

 quently to check exuberant growth by pruning : but to this it 

 can be replied, that the purpose of pruning is not so much to 

 check the energies of the plant, as to divert them to the pro- 

 duction of flowers end fruit ; while the coccida; attack not only 

 the fruiting branches, but the fruit itself, injuring the very 

 parts we desire to protect. 



{To he Continued.) 



