Spore Prints from Individual Phialides of Verticillium spp

Abstract

STERILE soil-extract agar pH. 4 (without mineral or organic additions) is allowed to set in a Petri dish. Using a fine rod finished off at the tip into a small glass bead, the agar surface is streaked with the given spore suspension or smear, care being taken to avoid breaking the surface. When phialospores are being produced in appreciable numbers, rectangular pieces of coverslip are placed flat on the surface of the agar close to and on opposite sides of the streak, and entire coverslips are then rested on them so as to cover the streak. Using a 1/5 obj. and ocular × 10 the upper surface of the coverslip is first brought into focus. Downward racking with the fine adjustment is then continued until phialides and spores are observed at or near the underside of the coverslip. Many upwardly directed phialides will have been caused to deposit their spores against the coverslip by this means, and in many cases the points of the phialides may be observed beside their own spore or spores. Phialides at a lower focus can also be caused to deposit their spores if the lens is pressed gradually down on the coverslip by means of the fine adjustment. In fact, it is quite possible, first to observe individual phialides bearing a spore mass, and then to pick off these spores by pressing the coverslip against them. The spore or spore masses may then be observed at a higher focus lying on the coverslip, and by again focusing downwards their previous relation to the now sporeless phialide-tips may be checked.