corresponding to homologous positions 487, 648, and 1389, respectively, of the S. cerevisiae SSU rRNA sequence J01353. Diversispora C. Walker & Schuessler, gen. nov. Etym.: Referring to the diverse nature of the spores found within the order to which the genus lends its name. A generibus ceteris in Glomeromycota distincta combinatione sporae glomoideae, sporae tunicis internis flexibilibus, ele- mento tunicae internae in solutione Melzeri non colorans, scutello germinationis absens, et sequentio DNA differenti. Typus : Glomus spurcum C. M. Pfeiff., C. Walker & Bloss 1996. Differs from other genera in the Glomeromycota in possessing glomoid spores with a spore wall structure consisting of a thin outer wall, a laminated structural wall, and a flexible inner wall not reacting with Melzer’s reagent, germination not preceded by formation of a germination shield, and specific SSU rRNA gene se- quence signatures, for example CYCATTRGYCAG- GCTTAATTGTC, TATTGGCATTTAGYCA, and CTTTGGATTRGGGTTTAGGGRTC, corresponding to homologous positions 649, 1387, and 1673, respect- ively, of the S. cerevisiae SSU rRNA sequence J01353. Diversispora spurcum (C. M. Pfeiff., C. Walker & Bloss) C. Walker & Schuessler, comb. nov. Glomus spurcum C. M. Pfeiffer, C. Walker & Bloss, Mycotaxon 14 : 374 (1996). Oehl, F. & Sieverding, E. (2004) Pacispora, a new vesicular arbus- cular mycorrhizal fungal genus in the Glomeromycetes. Journal of Applied Botany – Angewandte Botanik 78 : 72–82. Schu¨ßler, A., Schwarzott, D. & Walker, C. (2001) A new fungal phylum, the Glomeromycota : evolution and phylogeny. Myco- logical Research 105 : 1413–1421. Walker, C., Blaszkowski, J., Schwarzott, D. & Schu¨ßler, A. (2004) Gerdemannia gen. nov., a genus separated from Glomus, and Gerdemanniaceae fam. nov., a new family in the Glomeromycota. Mycological Research 108 : 707–718. Christopher Walker 1 and Arthur Schu¨ßler 2 1 Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK. 2 Institute of Botany, TU Darmstadt, Schnittspahnstrasse 10, D-64287 Darmstadt, Germany. DOI: 10.1017/S095375620424117X ASCOBOLUS IMMERSUS SPORE-GUNS DEVELOP 3 ATM PRESSURE The concept of forcible discharge of asci is familiar to all mycologists, but just how great are the pressures developed within indvidual asci ? Fischer et al. (2004) measured the turgor pressure within asci of Ascobolus immersus using a microprobe and determining the pressure needed to indent the ascus wall with a minia- ture strain gauge. The turgor developed ranged from 23–89 mN (or MPa), with a mean of a staggering 0.31 mN mm x2 , equivalent to about 3 atm. While the results are in general consistent with earlier research conducted by Buller and Ingold, their earlier calcu- lations were based on data from derived observations. This is the first time microprobes have been used for direct measurements, and the results are consequently incontestible. Interestingly, the force needed to propel the ascospore mass in this species to distances observed in practice was calculated as 0.2 MPa, the difference being ascribed to loss of pressure as the ascospores pass through the ascus apex. A mathematical model con- structed from the data indicates that the ascospores discharge at 0.32 m s x1 , accelerating ‘at thousands of g ’, comparable to ballistospore discharge but way ahead of acceleration recorded in other organisms such as the froghopper. Analysis of the ascus sap suggests that glycerol was the major osmolyte involved in the development of ascus turgor pressure, accounting for 0.1 MPa of the osmotic pressure found. Fischer, M., Cox, J., Davis, D. J., Wagner, A., Taylor, R., Huerta, A. J. & Money, N. P. (2004) New information on the mechanism of forcible ascospore discharge from Ascobolus immersus. Fungal Genetics and Biology 41 : 698–707. Mycological Research News 982