BLEPHAROPLAST. The blepharoplast is the organ which gives rise to the cilia of sperms. While it cannot be said that all cilia are developed from blepharoplasts, it is equally true that blepharoplasts do not occur except in connection with cilia. Usually, ble pharoplasts are very small, Mfg of an inch, or even less, in diameter; but in Ginkgo, the Maiden Hair Tree, they are much larger, and in the cycads they reach a diameter of TAR/ of an inch. The appearance and be havior of the blepharoplast during the forma tion of sperms is well illustrated by the com mon liverwort, Marchantia (Fig. 1). Toward the end of the spermatogenesis, in the cell which is to produce two sperms, two blepharo plasts appear (Fig. 1, A), The two ble pharoplasts give rise to the spindle fibers as the nucleus divides (B). After the nuclear division, the protoplasm divides obliquely and in each new cell the blepharoplast moves to one of the pointed ends (C). These two cells are the very young sperms. From the ble pharoplast of each of the young sperms, two cilia grow out (D). The protoplasmic and nuclear portions of the sperm now elongate and become indistinguishable while the ble pharoplast itself also becomes somewhat elongated and very slender. At maturity the two cilia become much longer than the body of the sperm (E; s, body of sperm; c, cilia).
In the ferns, the development of the sperm and the early development of the blepharo plast are similar, but in later stages the ble pharoplast becomes more elongated and gives rise to a large number of cilia. In the scour ing rush, Equisetum, the development of the blepharoplast is more complex. The early stages are about the same as in the liverwort and the fern, but after the blepharoplast has begun to elongate, it breaks up into a large number of granules from which the numerous cilia develop. The granules soon fuse again and form a solid band. The largest sperm in either the plant or animal kingdom is found in the cycads, the most familiar representative of which is the Sago Palm (Cycas revoluta), whose rigid, dark green leaves are in such demand on Palm Sunday and on funeral oc casions. The cycad sperm reaches a diameter
of of an inch and, consequently, is visible to the naked eye. The blepharoplast, which in the spherical condition may reach a diameter of rolinf of an inch, breaks up into an immense number of granules; the granules then fuse and form a spiral band from which thousands of cilia arise. Figs. 2 and 3 repre sent the principal features of the process in the African cycad, Stangeria. In Fig. 2, three of the pollen tubes show a rounded cell with two blepharoplasts surrounded by radia tions. In the lower right hand tube, the rounded cell has divided, forming the two young sperms. In Fig. 3, the blepharoplast has developed into a spiral band bearing in numerable cilia. The sperms, at this stage, are actively swimming and are just about to enter the eggs.
With the exception of the red alga, all plants below this level have swimming sperms; but in all the Gymnosperms, except the cycads and Ginkgo, and in all the Angiosperms, the swimming habit has been lost. It is worthy of note that the swimming habit reaches its highest and most complex development just as it disappears.
It has long been debated whether the ble pharoplast is a centrosome or not. In our opinion, the blepharoplast is a centrosome which, in its later stages, has assumed peculiar f unctions.
Bibliography.— Chamberlain, C. J.,