Orienting Minute Objects for Sectioning in a Definite Plane

Minute objects can be prepared for sectioning in a definite plane by a method which reembeds them directly on the cutting block under a dissecting microscope. By melting the paraffin immediately around the specimen, the latter can be oriented with reference to the planes of the block. After trimming, the block can be oriented squarely with reference to the microtome knife. Objects as small as 0.2 mm. have been cut successfully. The material sectioned included carpel primordia of Lathyrus, and young embryos, shoot apices and young axillary buds of Pinus. The technic is simpler than most methods previously suggested and it permits good control over the plane of sectioning.