7. In further studies on the B-type chromosomes in maize the number in individual plants has been increased to 32-35, with no marked decrease in plant vigor but with an appreciable decrease in fertility among these extremely high numbered B-type plants. Both Florida and Durango teosinte occasionally have B-type chromosomes which are morphologically identical with those in maize, and exhibit the same synaptic behavior and breeding relationships. Plants of Florida teosinte with 5 B-type chromosomes and plants of Durango with as many as 10-12 have been obtained by inter-crossing plants with lower numbers. From an extensive survey of chromosome morphology in various stocks of maize and teosinte, primarily for the purpose of determining the origin of the B-type chromosomes, an extremely wide variation in prophase morphology in different stocks has been noted; maize stocks with as many as 13-14 sizable knobs and others with as few as 1 or 2 have been discovered, also Durango and Florida teosinte stocks with very few and other stocks with numerous knobs. However, a careful search for a chromosome arm in these diverse stocks similar to or identical with the B-chromosome has been fruitless thus far. This suggests that the B-chromosome may be a composite of several parts from different regions of the same or different A-chromosomes.