1916] Gilkeij: A Revision of the Tuherales of California 313 



Tuber (Eutuber) levissimum sj). nov. 



Plate 30, fig. 31 



Tuher Borchii Hk. non Vitt., Proc. Cal. Acad. Sci., 3d ser., vol. 1, no. 8 

 (1899), p. 272. 



Ascocarp clay-brown, 2 cm. in diara., regular ; surface smooth : 

 gleba lighter brown than cortex ; veins large, inconspicuous in color ; 

 cortical tissue barely pseudoparenehymatous, composed mostly of 

 more or less closely coalesced irregular hyphae, becoming less con- 

 nected toward hymenium ; outer cells slightly broken away, making 

 surface of ascocarp very minutely scabrous, this character visible 

 only under compound microscope; thickness of peridium 840/x.; venae 

 internae and tissue between asci of compact, more or less closely 

 coalesced parallel hyphae, 5-6;u. thick ; venae externae filled with 

 similar hyphae loosely arranged, not parallel, unconnected ; asci sub- 

 globose to globose, 50-80 by 70-1 00ft; 1-4-spored ; spores globose- 

 ellipsoid, 32-48 by 36-52/^, alveolate, alveoli irregular in size and 

 number on spore, 3-10 by 4-13 across diameters ; sculpturing 4/a thick. 



"In rich, damp loam, about 9 in. below surface, Mav, 1912." 



No. 338, U. C. Col. Type. C. F. Drew. 



"Among decaying leaves of oak, Mt. Tamalpais, Marin Co., Calif., 



June." No. 54, Hk. Col. 



This species agrees very closely in shape and color of ascocarp ; 

 venation ; and shape, size and sculpturing of the spores, with the de- 

 scriptions of Tuher Borchii Vitt. The alveoli of the spores of the 

 latter, however, are described as generally very regular in form. In 

 the Californian material this is found to be the case in perhaps one- 

 half of the spores of a plant. In the others irregularity in size and 

 shape exist to a noticeable degree. No evidence of pubescence or 

 spots of dark color on the surface of the ascocarp is found, but as 

 these are both described as early characters in T. Borchii which dis- 

 appear with maturity their absence is not necessarily important. No 

 mention is made in descriptions of T. Borchii of the very thick peri- 

 dium nor of the small amount of pseudoparenchyma in the cortex ; and 

 the description of the subcortical layer as composed of irregular, loose, 

 interwoven hyphae does not agree with that layer in the Californian 

 plants, in wliicli it is a regularly arranged, generally compact tissue of 

 more or less coalescing hyphae. 



Of the Harkness material only lliree portions of specimens are 

 now present in the collection, making impossible the determination of 

 points such as size. The material in the University of California her- 

 barium, being more ample in quantity and in much better condition, 

 has been selected as the type. 



