of Danais Archippus. 101 



■would probably soon be seen, or tlieir depredations on the 

 food plant must be soon discovered ; but although this is not 

 a fatal objection, the undeniable introduction of the genus 

 Asclepias by the agency of man is one of the most im- 

 portant necessities for the continuance of the existence of 

 this butterfly, however or by what means its own dispersal 

 has occurred. 



Having glanced at the means of dispersal, we will now 

 briefly examine the conditions that must be favourable to 

 the survival of this butterfly in a new habitat. 



Istly. The presence of its food plant. — It is scarcely 

 necessary to remark that however a butterfly may be dis- 

 persed by winds, waves or the agency of man, without its 

 food plant also exists, it has little chance of surviving in 

 a ncAV habitat, excepting in the rarer instance of adapta- 

 bility to a new food in another genus or family of plants. 

 Now the favourite food of D. Archippus is the various 

 species of the genus Asclepias, to one of Avhich, however, 

 "^. phytolaccoides^^ according to Mr. Iviley, it shows a 

 " wonderful dislike" As regards the range of this genus 

 Ave cannot do better than quote from the " Genera Plan- 

 tarum." " Species ad 60, plerteque Americaa borealis 

 Mexico inclusa incolce, paucse in America centrali V 

 australi obvire, 2 Africante, 1 per regiones calidiores utrius- 

 que orbis late dispersa, in plerisque tamen locis inquilina." 

 This wide ranging species is the A. curassavica, Linn., 

 and which in the South Sea Isles has been recorded from 

 Eromanga, New Hebrides and the Tongan and Society 

 Isles, " probably introduced as not known to the older 

 botanists." * 



Professor Westwood reminds me that no Asclepias is 

 found wild in Europe. The original habitat of the genus 

 Asclepias agrees Avith that of D. Archippus, for, as 

 De CandoUe observes in treating of ^. curassavica as found 

 in the Society Isles, " mais il me parait evident qu'il 

 s'est cchappe des jardins, ou qu'il a ete apporte dans 

 ces localitcs. On salt combien cette plante se multiplie 

 aisement;" and as the majority of the species of Asclepias 

 are American, he further remarks, " ce qui me parait 

 indiquer assez clairement I'originc."! A. fructicosa is 

 recorded from the Azores, but is a South African species, 

 and Mr. Watson considers it is there only as a 



* B. Secman, Flora Viticnsis, p. 101. 

 t GoDgraiihic Botuiiiqno, tdinc ii. p. 7f 



