516 



BLIGHT. 



Now, if we carefully feed the blight of an apple- 

 tree, for instance, under a glass, we shall find that it 

 ultimately becomes a small moth, which moth, after 

 and even without impregnation, if it be a female, 

 deposits eggs of a sensible size, not fertile, of course, 

 in the latter case. Setting aside, therefore, other 

 considerations, it cannot be doubted, that if these 

 eggs were carried about by the winds, they would 

 be evidently visible ; but no such thing occurs ; all 

 that is perceived is " an easterly wind, attended by 

 a blue mist," or " a peculiar haze or rnist, loaded," as 

 it is asserted, " with poisonous miasm." And the 

 same may be said of the eggs of other species of 

 blight, that is, of insect blight, even of the aphides. 

 They are all sufficiently large to be visible by the 

 microscope, if they were wafted about in the air, and 

 yet none are to be perceived. Moreover, it is to be 

 observed, that in the case of the blight of our fruit- 

 trees, it is perfectly well ascertained, that the eggs 

 from which the grubs are produced in the spring are 

 deposited in the preceding autumn ; whence it would 

 follow, that if they were merely dropt into the air, 

 they would necessarily be floating until the following 

 spring, during six months wintry weather a rather 

 improbable thing, we should suppose, regard being also 

 had to the great specific gravity of eggs of insects. 



But this hypothesis, in several other points of view, 

 seems equally irreconcileable with nature. If the eggs 

 from which blight is supposed to be produced were 

 really floating in the air, it would necessarily follow 

 that immense numbers of such eggs must perish, such 

 only surviving as happened to be wafted to those 

 particular parts of a tree to which it is to be observed 

 that the blight attaches itself; this will invariably be 

 found to be the tender young shoots and buds. But 

 this supposition is so perfectly at variance with that 

 beautiful regulation in nature by which nothing is 

 made in vain, that it will only be necessary, for its 

 more satisfactory refutation, to notice the great anxiety 

 and care which parent insects invariably manifest 

 in depositing their eggs, even where they are com- 

 pelled, for the fulfilment of this object, to visit an 

 element totally different from that in which they are 

 accustomed to pass their perfect state ; a single 

 example of which may be noticed in the dragon-fly 

 (libellula), the females of which may constantly be 

 observed standing upon the edge of a pond, &c., 

 thrusting their long abdomen a considerable depth 

 into the water, in order to place their eggs in se- 

 curity, in such situations where the young, when 

 hatched, will find a due supply of food. 



But it may be urged, that although placed in such 

 particular spots by the parent insect, the eggs pro- 

 ducing blight are liable, during the six months which 

 are passed in this state, to be carried off by the 

 violence of the winds and weather. If this, however, 

 were the case, all the anxiety of the parent fly would 

 be in vain. Nature has consequently provided against 

 this, by endowing the parent fly with the instinct to 

 cover the eggs with various kinds of envelopes, either 

 with webs spun by themselves, or with materials 

 derived from their own bodies, as in the case of 

 various moths, &c., or from adjacent substances. 

 Most commonly, however, the female leaves her 

 cluster of eggs without any other covering than the 

 varnish with which they are besmeared in their 

 passage from the oviduct, by means of which they 

 are not only firmly gummed to the substance upon 

 which they are placed, but are also defended from 



the cold and winds of winter, so as to allow the 

 young grubs to burst forth into life and activity in the 

 following spring, carrying destruction in tboir'path. 



Thus have we, as we trust satisfactorily, shown 

 that the eggs from which the various kinds of bli-ht 

 are produced, do not float at random in the wind, and 

 that there is not, as it is said, " a blight in the air." 

 We have now, therefore, to consider the prevalence 

 which certain winds appear to have in giving birth 

 to grubs enclosed in eggs deposited by the parent 

 insects upon the spots in which the blight is observed, 

 and here the common observation of mankind, 

 although employed upon effects instead of causes, 

 must be allowed to have some weight. It is not 

 perhaps to be doubted, that the action of certain 

 winds, depending upon variations in temperature, and 

 other metereological changes, which may be even 

 entirely unappreciable by our most minute observa- 

 tions, has the power of bringing forth what is termed 

 blight, the instantaneous appearance of which in 

 vast numbers, at the same time, and the consequent 

 ravages which they occasion being noticed by the 

 commonest observer of nature ; hence it is that the 

 sudden appearance of these destructive myriads is at 

 once attributed to the wind, to which, in fact, it is 

 partially attributable, but which, amongst the ignorant, 

 at once obtains the credit of generating and depositing 

 the blight. It has been generally considered by 

 naturalists, that the eggs deposited in the preceding 

 autumn, having been laid at the same time, and ex- 

 posed to similar atmospheric changes, are necessarily 

 hatched at the same time in the spring, when, in fact, 

 intelligence is obtained by the enclosed grubs, from 

 the peculiar state of the air, that the fitting time for 

 bursting forth from the egg is arrived. This opinion, 

 which, in fact, is by far the nearest to truth of all 

 which have been hitherto given, does not, however, 

 account for the great size which the supposed newly- 

 hatched blight are observed to have attained. The 

 subject, however, has recently been submitted to a 

 minute series of observations by Mr. Lewis, whose re- 

 searches will be found detailed in the first number 

 of the Transactions of the Entomological Society. 



We have said, that swarms of plant-lice upon rose- 

 trees, and other shrubs, are often considered as blight, 

 and intimately connected with them, as well as the 

 preceding subject, is what is termed honey-dew, 

 respecting which Dr. Good observes " I have seen, 

 as probably many who read this work have also, a 

 hop ground completely overrun and desolated by the 

 aphis humuli, or hop green louse, within twelve hours 

 after a honey-dew (which is a peculiar haze or mist, 

 loaded with poisonous nriasni) has slowly crept 

 through the plantation, and stimulated the leaves of 

 the hop to a morbid secretion of a saccharine and 

 viscid juice, which, whilst it destroys the young shoots 

 by exhaustion, renders them a favourite resort for this 

 insect, and a cherishing nidus for myriads of little 

 dots that are its eggs." Now, the opinion which we 

 have already given as to the action of peculiar winds 

 upon the blight-egg's will enable us satisfactorily to 

 explain the sudden appearance of the aphis humuli 

 within so short a time after the appearance of this 

 "peculiar haze," without referring it to the circum- 

 stance of the eggs of these insects being carried about 

 by such wind. Indeed, it seems evident that Dr. 

 Good considered that the action of the " peculiar 

 haze" was directed only to stimulating the leaves of 

 the hop to a morbid secretion, which it is not to be 



