The Nutrition of the Egg in Zamia

FOR some time previous to the cutting off of the ventral canal cell, the central cell in most gymnosperms is surrounded by large prominent cells called the "jacket cells," which contain particularly large nuclei. The inner walls of the jacket cells, in contact with the egg, are pierced by numerous pores (fig. 2). During the rapid growth of the central cell the jacket cells and their nuclei are prominent; but during the period of free nuclear division in the embryo the jacket becomes less conspicuous, and finally becomes indistinguishable as a definite nutritive layer. It is evident that the jacket cells contribute to the growth of the central cells, and afterward to the growth of the egg and proembryo. The passage of various contents of the jacket cells into the egg has been described by several observers. Goroschankin (4) says in regard to Ceratozamia: " In fresh preparations mounted in water, each canal is seen to be filled with fine protoplasm that passes over sometimes into the protoplasm of the neighboring cells and sometimes into the protoplasm of the egg cell. Transverse and longitudinal sections of fruits which were carried up with strong alcohol showed me the following: under the action of the alcohol the protoplasm of the surrounding endosperm sheath seems wholly smooth or with scarce observable projections on the side nearest the egg. But as for the protoplasm of the egg, it appears covered with projections the length of which equals nearly or wholly the length of the canals. Afterward I began to make tangential sections of the egg from alcoholic preparations. Now I was able to see the sieve plates in the canal ... . From my observations on the egg wall in the cycads, the following conclusions were reached: