A system for stacking into containers flat articles received in a shingled stream, the flat articles being disposed essentially normal to the bottoms of the containers into which they are stacked; mechanism is provided for rapidly diverting the shingled stream of flat articles from the rear of a just filled container to the front of the next empty container in a line of moving containers to feed flat articles into successive containers without interruption; containers having elongated slots in the ends are provided to facilitate the rapid shifting of the article stream from container to container in a line of containers; there also is provided a mechanism to generate a gap in the shingled stream of flat articles to facilitate transfer of the stream from a filled container to an empty container; there further is provided mechanism for diverting the shingled stream of flat articles before it reaches the containers to sample the flat articles or to reject the flat articles should they be defective; also provided are novel container conveyor systems for conveying containers to the loading station to accommodate the stacking mechanism.