1921] Wheeler: Some Social Beetles 41 



have only two or three, the largest hardly more than a dozen 

 leaves. These are dark green, smooth and somewhat shining, a 

 except at the base, where it forms a fusiform swelling two to 

 four inches in length and a third to half an inch in diameter. The 

 longer, more distal portion of the petiole bears six to eight pairs 

 of broadly lanceolate leaflets, which are not drooping or pendant. 

 The stipules at the base of the petiole are small and inconspicu- 

 ous. The sun form (Fig. 4) is much more vigorous and has 

 numerous branches at or near the summit of the long, slender, 

 foot or less in length. The petiole (Fig. 5a) is very slender 

 smooth, gray-barked trunk. The leaflets are pendant, more 

 crowded, much coarser, brighter green, with more rugose surfaces 

 and the petiole is thicker, with a large, three-cornered basal swell- 

 ing more gradually continued into the leaflet-bearing portion 

 (Fig. 5b) . The cavity of the petiole also extends nearly through- 

 out its length instead of being confined to the basal, swollen 

 portion, and there are also cavities in the branches near each 

 leaf. The stipules are large and conspicuous and palmately 

 multifid. Forms of the plant' intermediate between the shade 

 and sun forms were rarely seen. The specific identity of the two 

 forms was proved by finding young shoots of the typical shade 

 form growing from the trunk of a large sun tree in an abandoned 

 cassava patch at points where the wood had been cut back by 

 the natives. 



The Tachigalia Biocoenose. 



The interrelationships of the various organisms constituting 

 that portion of the Tachigalia biocoenose with which this paper 

 deals, i. e., the numerous insects with their parasites and satel- 

 lites, that infest the young shoots and leaves, are represented in 

 the accompanying diagram (Plate II). It will be seen that the 

 portion of the plant which forms what may be called the center 

 of the biocoenose is the leaf-petiole, and it is, of course, the 

 peculiar structure of this organ that determines the specific 

 relations of the various insects to the host-plant and is, there- 

 fore, the key to an analysis and understanding of the whole living 

 complex. As Prof. Bailey will publish a detailed account of the 



