The study was financially supported by the Swiss National Science Foundation (Grant 8220-033188). G. V. was supported by 60% MURST grant (to G. Zanzucchi). The authors give many thanks to James J. Pospichal for reviewing part of an early version of this manuscript, and J. Mitchener Covington for providing us with BugWare. We thank Kim Riddle for her time and assistance during the work on the scanning electron microscope. We thank Mario Cachao and José-Abel Flores for thorough reviews that resulted in an improved paper.