THE FLORAL WOELD AND GARDEN GUIDE. 



17 



Fancy and- Intermediate. — Archduchess 

 Augusta, dark crimson, veined bhie ; 

 Caryophylloides, bhish, striped with car- 

 mine ; Comto de Paris, sahnon pink, 

 edged white j Era Amolda da Brescia, 



red, curiously marbled with white ; !M;ku- 

 lata Perfecta, varies from white, with rt so 

 stripes, to rose, with wliite stripes ; Priu- 

 cesse de Lamballe, rosy white, with car- 

 mine stripe, shade of sulphur in centre. 



NATURAL HISTORY OF PLANT LICE. 



BY PROFKSSOK H. HUXLEY, F.K.S. 



A LEARNED French naturalist, M. Duvau, 

 proposed, many years ago, to term the 

 middle of the 18th century "Fepoque 

 des Pucerons," and the importance of the 

 phenomena which were at first brought to 

 light by the study of these remarkable 

 insects, renders the phrase " epoch of Plant 

 lice," as applied to this period, far less 

 whimsically inappropriate than it might at 

 first sight seem to be. After a brief sketch 

 of the mode of life of these plant lice, or 

 Aphides, as they are technically termed — of 

 the structure of their singular piercing and 

 sucking mouths, and of their relation to 

 what are called " blights," the circumstances 

 which have more particularly drawn the 

 attention of naturalists to these insects, 

 were fully detailed. It was between the 

 j'ears 1740, and 1750, in fact, that Bonnet, 

 acting upon the suggestion of the illustrious 

 Reaumur, isolated an Aphis immediately 

 after its birth, and proved to demonsti-ation 

 that, not only was it capable of spontane- 

 ously bringing forth numerous hving j'oung, 

 but tbat these and their descendants, to 

 the ninth generation, preserved a similar 

 faculty. 



Observations so very remarkable were not 

 likely to pass unheeded, but. notwithst<inding 

 the careful sifting which they have received, 

 Bonnet's results have never bem questioned. 

 On the cintrary, not only have Lyonnet, 

 De Geer, Kyber, Duvau, and others borne 

 ample testimony to their accuracy, but it 

 has been shown that, under favouraiile con- 

 ditions of temperature and food, there is, 

 practically, no limit to this power of asexual 

 multiplication, or, as it has been conveniently 

 termed, " agamogenesis." Thus Kyber bred 

 the viviparous Aphis Dianthi, and Aphis 

 Ros» for three years in uninterrupted suc- 

 cession ; and the males, and true oviparous 

 females of the A. Dianthi have never 3-et 

 been met with. The current notion that 

 there is a fixed number of broods, " nine or 

 eleven," is based on a mistake. As, under 

 moderately favourable conditions, an Aphis 

 comes to maturity in about a fortnight, and 

 as each Aphis is known to be capable of 

 producing a hundred young, the number of 

 the progeny which may eventually result 



even from a single Aphis during the six or 

 sewn warm months of the year, is easily 

 calculated. M. Tougard's estimate, adopted 

 (and acknowledged) by Morren, and copied 

 from him by others, gives the number of the 

 tenth brood as one cfuintUlion. Supposing 

 the weight of each Apliis to be no more than 

 1,000th part of a grain, the mass of living 

 matter in this brood would exceed that in 

 the most thickly populated countries in the 

 world. The ai;amogenetic broods are either 

 winged or w ingless. The winged forms at 

 times rise into the air, and are carried away 

 by the wind in clouds ; and these migrating 

 hordes have been supposed to be males and 

 females, swarming like the ants and bees ! 

 During the sunnner months, it is unusual to 

 meet other than viviparous Aphides, whether 

 winded or wingless ; but ordinarily, on the 

 approach of cold weather, or even during 

 warm weather, if the supplies of food fall 

 short, the viviparous Aphides produce forms 

 which are no longer viviparous, but are 

 males, and oviparous females. The former 

 are sometimes winued, sometimes wingless. 

 The latter, with a single doubtful exception, 

 are always wingless The oviparous females 

 laj' their egirs, and then, like the males, die. 

 It commonly happens also that the vivip^'r- 

 ous Aphides die, and then the eggs are left 

 as the sole representatives of the species ; 

 but. in mild winters, many of the viviparous 

 Aphides inere'y fall into a state of stupor, 

 and hybernate, to re-awake with the return- 

 ing M'armth of spring. At the same time 

 the eggs are hatched, and give rise to vivi- 

 parous Aphides, which run through the same 

 course as before. The species Aphis there- 

 fore is fully manifested, not in any one being 

 or animated form, but by a cycle of such, 

 consisting of— 1st, the egg; 2d, an indefinite 

 succession of viviparoiis Aphides; 3d, males 

 and females eventually produced by these, 

 and giving rise to the egg again. 



The phenomena which have just been 

 described, were long supposed to be isolated ; 

 but numerous cases of a like kind, some 

 even more remarkable, are now known. 

 Among the latter, the speaker cited the 

 wonderful circumstances attending the pro- 

 duction of the drones among bees, as 



