ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
507 
no differentiation of female apparatus takes place ; no corpuscles or 
special egg-cells are formed, nor any autipodals ; the protoplasm of the 
embryo-sac divides into a parietal layer of primordial cells (with central 
vacuole), which appear to be altogether equivalent, and which represent 
so many egg-cells capable of impregnation. 
The course of the pollen-tube is easily followed. Its nucleus 
probably gives off a smaller vegetative nucleus soon after its entrance 
into the tissue of the nucellus. The two nuclei continue very near to 
one another ; while the vegetative nucleus or prothallium-cell remains 
unchanged, the generative nucleus increases greatly in size, and divides 
into two of equal value ; the apex of the pollen-tube has now (in G. edule ) 
entered the apex of the embryo-sac ; while in G. neglectum it appears to 
make a curve to avoid the apex of the sac, and becomes closely applied 
to its lower part. The micropyle closes after impregnation. After the 
pollen-tube has entered the embryo-sac, its vegetative nucleus disappears, 
while each of the two generative nuclei surrounds itself with a proto- 
plasmic membrane, and the nucleus in each generative cell divides into 
four or possibly into eight. The author was unable to detect the actual 
coalescence of the male and female nuclei ; but in the male generative 
cells, in addition to the four comparatively large male nuclei, a number 
of small nuclei were detected, which the author regards as the nuclei of 
the primordial egg-cells which have wandered into the male generative 
cells ; and the coalescence must take place within the male generative 
cell. 
After the entrance of the pollen-tube the parietal layer of protoplasm 
of the embryo-sac in which the female primordial cells are imbedded, 
breaks up into an endosperm tissue ; and the central vacuole also 
becomes replaced by the endosperm, which is wanting only in the parts 
occupied by the male cells or the resulting embryos. 
The development of the embryo is described in detail, including the 
formation of a pro-embryo or suspensor. Although there is such large 
scope for poly-embryony, the author found no example of more than 
one embryo becoming fully developed. 
Very little is known of the corresponding processes in the other 
genera of Gnetaceae, Welwitschia and Ephedra. The author regards 
Gnetum as representing the highest type of the order ; the fact that no 
endosperm is formed before impregnation is an advance on other 
Gymnosperms. The presence of a large number of fertile embryo-sacs, 
and the absence of antipodals, indicate some analogy with Casuarina. 
Herr Karsten holds that the processes described above finally 
negative the theory that the antipodals are a survival of the prothallium 
of Vascular Cryptogams; he regards them rather as a degenerate and 
functionless female sexual apparatus. According to this view there are, 
in the embryo-sac of Angiosperms, two sexual apparatuses, of similar 
origin, the vegetative nuclei of which coalesce, but one of which is 
altogether abortive. Both antipodals and egg-apparatus (embryonic 
vesicles) consist of an archegone reduced to a single cell. 
Embryogeny of Tectona.* — Herr S. H. Kooders describes in detail 
the mode of development of the embryo of Tectona grandis (Verbenaceae), 
* Natuurk. Tijdschr. Nederl. Iudie, li. (1891) 8 pis. See Bot. Centralbl., xlix. 
(1892) p. 271. 
