62 
extending its range and that the gall-producer has not been 
able to keep pace with it (idem). D. The problem, whether 
plants found in islands, separated from the proper area of the 
plant, should be regarded as relicts or as arrivals, might be 
solved also by means of the galls found on them. In any case 
the occurrence of galls with slow-moving gall-producers might 
point to those plants being relicts on those islands. 
Part of these rules are already found in Hieronymus ‘). 
The study. of the Krakatau-galls does not confirm these hypo- 
theses. The gall-producers to be found on Krakatau are all slow- 
moving gall-insects. 
All the plants have arrived but lately and yet inal are found on 
them in abundance. Nature heeds no man-framed rules. When 
on islands certain plants occur without galls, whilst the same 
plants do bear galls in other localities, the only justifiable in- 
ference is that the gall-producers have not yet been conveyed 
to those islands. On my expedition to the islands south of 
Celebes I found on a very small level coral-island a number of 
small Casuary-trees (chemara) and these teemed with the galls 
already described by me’). On Krakatau, where the Casuarinae 
have already reached a considerable height (there are trees 
more than 110 ft. high) I did not find a single gall, though I 
paid spécial attention to them. On the contrary I found a large 
number of Polanisia viscosa with numerous galls on the same little 
coral-island; nearly all the plants were strongly infected. Now 
this herb thrives for preference on fallow ground; also on that 
little island they grew in an abandoned maizefield that had 
belonged to a small kampong (native village). The nearest is- 
— are ar a from it and on these | did not find the 
an “The: fact bnivesbe that on an island entirely devastated, so 
- — ‘different nse occur after a —_= of time rela- 
: He 5, toa Beitrag zur Kenntnis der europ. Zoocecidien und der Verbrei- 
€ _Jahresber. Bichles. Ges. f. vaterl. Kultur, 1890. Ergiinzungsheft, 
2) Bigs Gallen aus a ete. Bull, a. Jard. Bot. J naperaene Série II, 
