388 MR. H. H. W. PEARSON ON SPECIES OF 
the outer pitcher in all four species and in every specimen 
examined. Curiously enough, no trace of such a mycelium could 
be found on either wall of the inner pitcber in any species. It may 
be that the secretion of the glands of the inner pitcher is of such 
a nature as to limit the growth of the fungus to the outer pitcher. 
The explanation of this remarkable occurrence I must leave to a 
more fortunate investigator. I can only draw attention to the 
extraordinary similarity between the hyphe of the rosette and 
the “ Stranganschwellungen ” and “ Perlenfaden ” which Moller 
found in the “ fungus-gardens” of the South-American species 
of Atta*. Termites of both continents are fungus-growers T, 
but I am not aware that ‘‘fungus-gardens” have yet been 
described for any of the true ants in the Old World. 
Conclusion. 
The details of my suggested explanation of the adaptation of 
these double pitchers for the purpose of accommodating their | 
ant-population will undoubtedly require modification when the 
living plants can be studied. But the general conclusion that 
they are peculiarly modified in such a manner as to render them 
specially attractive to ants is, I venture to think, hardly open to 
doubt. How is the plant the better enabled to compete in the 
struggle for existence by the adoption of this highly specialized 
form of pitcher? This question is one of peculiar difficulty, 
and impossible of solution except by a study of the natural 
conditions in which the plant lives. An obvious suggestion is 
that this complicated pitcher is a response to a demand for an 
increased economy of water in a xerophytic environment. The 
condensation of transpired water upon the profusely branched 
root-system in an almost closed bag must be more effectively 
attained than in the less complex pitcher of D. Rafflesiana. 
That our four species are markedly xerophytic is sufficiently 
indicated. The foliage-leaves of D. pectenoides are very 
small; D. complex is described by Griffith as leafless; the 
specimens of the other two species are also without leaves. 
But it is impossible to pursue this subject further in the present 
* Moller, ‘ Die Pilzgirten einiger siidamerikanischer Ameisen ’ (Jena, 1893), 
Taf. 6. fig. 18. 
+ Haviland, G.D.,in Journ. Linn. Soc., Zool. xxvi. (1898) pp. 359-360, 
382-383, 
