The stems are the most potent part of the specimen. The caps have less psylocibin than the stems. If you bruise the fresh (and sometimes dry) specimen, you can

The stems are the most potent part of the specimen. The caps have less psylocibin than the stems. If you bruise the fresh (and sometimes dry) specimen, you can see it turn blue. That indicates the presence of psylocibin. The smaller the specimens, the more psylocibin per gram you will have in a dose as there is significant psylocibin even in tiny specimens, including ones that have barely formed caps.