1. Ceratozamia mexicana grows best in well shaded mesophytic conditions. 2. Any individual in passing from the seedling to the adult stage shows such a progressive change in its leaves, the leaflets becoming larger, broader, thicker, and more numerous, that descriptions of species based largely upon leaves are open to suspicion. 3. The ovulate strobilus shows considerable variation in the size and number of its sporophylls. 4. In addition to the primary haustorium, a system of secondary haustoria is developed later from the basal portions of the pollen tube. There are regularly two sperms, but occasionally four are produced. 5. A small ventral canal nucleus is present, but occasionally it enlarges and may fertilize the egg. It is suggested that this may explain the so-called hybrids obtained by Van Tieghem. In most cases fertilization occurs in the usual way. 6. Both suspensors and young embryos may unite, so that from five fertilized eggs there may come one to five embryos. In the mature seed, as found i...