1907.] Wheeler, Fungus-ijrowing Ants of North America. 767 



rock are exceedingly oppressive. Water is very scarce and the vegetation 

 is so sparse and stunted or of such a xcrophytic character as to yield little 

 shade except in the deeper canons. The trees and shrubs comprise such 

 species as the mountain cedar (Junipcrus sahinoides), several hackberrics 

 {Celtis hclleri, reticulata and pallida,) oaks (Quercus fii-fiformis breviloba and 

 schneckii), buckeyes (Ungnadia spcciosa and J^scidus octandra), dwarf 

 mulberry {Moms ccltidi folia), dwarf walnut (Juglans rupcitris), frijolillo, 

 or coral bean {Sophora secuudi flora), Texas persimmon (Brayodendron 

 texanum), madrona {Arbutus xalapensis var. texana), algerita {Berber is 

 trifoliata), Eysenhardtia amorphoides, Leucophyllum texanum, Rhus micro- 

 phylla and virens, and Ephedra antisyphilitica. During the spring the bare 

 rocks are beautiful v>ith a profusion of smaller plants {Gilia rigidiila, Castil- 

 leia, Salvia texana, Stillingia angustifolia, Palafoxia texana, Androstephium 

 violaceum, Camassia fraseri, Yucca rupicola and Nolina) 



It is only on the higher and more arid terraces that C wheeleri manages 

 to live and cultivate its fungus gardens, where long after other plants have 

 bloomed and deep into the winter the golden heads of Actinella scaposa nod 

 on their long stems. The nests are always under large stones covering a 

 little lingering moisture in the hard soil, which consists very largely of dis- 

 integrated limestone. Each colony comprises only a few dozen workers 

 and a single dealated female except during the spring and early summer, 

 when one finds also several callow workers, males and females and a variable 

 number of eggs, larv?e and pupse. The workers are nocturnal, at least 

 during the warm seasons of the year, a peculiarity which is indicated by 

 their yellow color. They are very slow in their movements and readily 

 "feign death." 



The excavations though extensive for such small ants, are unlike those 

 of Atta, Trachymyrmex and Mycetosoritis. A few rough and occasionally 

 branching galleries about 1-2 cm. in diameter run along the surface covered 

 by the stone, and descend vertically into the ground to a depth of 10-15 cm. 

 One of the surface galleries terminates in a small entrance at the edge of the 

 stone where its opening may be marked by a small crater. Irregular and 

 indistinct dilatations in the galleries represent the chambers of other Attii, 

 and in one of these dilatations, which is often fully exposed when the stone 

 is removed, or may be readily luicovered at a depth of a few cm., the single 

 fungus garden is found. This rests directly on the ground and is spheroidal 

 or ovate, usually about the size of a filbert or pecan nut, more rarely half as 

 large as a hen's egg. It consists of a delicate flocculent substratum made of 

 small vegetable slivers covered with a dense snow white mycelium. The 

 slivers average from 1-3 mm. in length and appear to have been torn from 

 the stems of herbaceous plants. They undergo no trituration or comminu- 



