8 ON PARASITES. 



some of whicli latter, however, it is found necessary to consolidate. 

 It is seen that there is hardly a species of plant or animal that does 

 jiot at some time support one or more species of parasite, yet until a 

 recent period very little positive knowledge was possessed concerning 

 them. That a class of organisms so intimately connected with 

 human welfare as these are found to be, should have remained so long 

 without scientific inquiry, might seem strange, were it not that many 

 of the phenomena connected with them are exceedingly obsciire, that 

 their habits are often repulsive, and that they are deficient in those 

 qualities which compel attention to the denizens of the desert and 

 forest, the flocks and herds, the lofty forest trees, the feathered 

 tribes and useful plants. 



A few hours, a single night often, has sufficed to usher into being 

 worlds of parasite cryptogams upon the cereal crops, to the entire 

 destruction of the farmer's hopes. Pamine even has resulted from 

 their malign luxuriancy of growth. Tet amazement and grief until 

 recently were the only emotions excited by these cryptogams. Their 

 effects were seen and deplored, but no rational investigation was made 

 into the nature and cause of the hliglit, as they were called. With 

 characteristic regard only for the cares and necessities of the 

 present, and carelessness of the future, agriculturists plodded on 

 the daily round of toil, hoping that some time the " blight" would 

 cease to destroy, and plenteousness again repay their labors. Not a 

 year passes that millions of dollars are not paid for the maintenance 

 of such cryptogams as the Uredo, Puccinia, Botrytis, Oidium, and 

 many other fungi, yet it is only now that the history of these parasites 

 is being investigated. In time, with the aid of collateral sciences, 

 among which, not the least important is meteorology, a strong hope 

 may be entertained of protecting plants from their destructive ravages. 



The investigations of naturalists have been equally successful among 

 animal as vegetable parasites. These creatures are found in vast 

 abundance upon vegetation from the proud forest tree to the humble 

 blade of grass. Of the many hundred species already known which 

 prey upon vegetation the aphides may be particularly alluded to on 

 account of their puny size, terrible voracity and powers of increase. 

 With a single grasp of the hand thousands of these insects may be 

 annihilated, so helpless are they in their own defence, yet by sheer 

 force of numbers they often thwart the most determined effort to 

 stay their ravages. The strange metamorphoses of this species of 



