ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
645 
were found to bo twenty-four ; and this is probably also the number in 
the sporophytic tissue. No centrospheres or centrosomes were seen in 
connection either with fertilisation or with any of the related processes. 
Embryology of Gnetum.* — Dr. J. P. Lotsy contributes the following 
notes on the embryology of Gnetum Gnemon. 
The female flowers in the purely female inflorescences have three 
envelopes ; those in the pseudo-androgvnous inflorescences two, with at 
first the rudiment of a third. Several embryo-sacs (megaspores) are 
formed ; multiplication of the nucleus takes place in them all ; but 
usually only one megaspore attains its full size. If unimpregnated, the 
embryo-sac becomes completely filled with endosperm. In the mature 
embryo-sac is a parietal j)rotoplasm-sac with numerous free nuclei. 
Before impregnation the embryo-sac becomes constricted into a smaller 
lower and a larger upper portion. In the lower portion a tissue 
is formed before the pollen-tube reaches the embryo-sac, which the 
author regards as a prothallium. No cell-division takes place in the 
upper portion of the embryo-sac. At the time when the pollen-tube 
reaches the wall of the embryo-sac, it contains a pollen-nucleus which 
is already disorganised, and two generative nuclei. One or more pollen- 
tubes enter the upper portion of the embryo-sac which contains the free 
nuclei, both the generative nuclei entering the sac. Each of the male 
generative nuclei coalesces with one of the free nuclei of the embryo- 
sac, so that two products of copulation result from each pollen-tube ; 
each of these “zygotes” then surrounds itself with protoplasm, and 
ultimately with a cell-wall. Some of the free nuclei form a rudimentary 
endosperm around the zygotes. The pollen-tubes may still be attached 
to the zygotes after these begin to grow. They first grow into long 
tubes (pro-embryos), the nucleus travelling to the apex. The pro- 
embryos either insert themselves between the prothallium and the wall 
of the embryo-sac, or enter the prothallium. This latter now presses 
aside the nucellar tissue and grows to a large size, with a small hollow 
at the apex corresponding to the upper part of the embryo-sac. In this 
upper portion the upper apices of the pro-embryos project, while the 
lower apices penetrate further into the prothallium. At this stage the 
seed falls from the tree. 
Embryology of Drosera.f — According to Prof. C. A. Peters, the 
mode of development of the embryo of Drosera somewhat approaches 
the monocotyledonous type. A sporogenous layer of four cells is pro- 
duced in the nucellus, but no tapete. Three of these cells soon become 
disintegrated, the fourth being the mother-cell of the embryo. The 
microsporange produces a tapete which originates and disappears in a 
similar way. From the first division of the pollen-mother-cell are 
produced two cells lying in close proximity, which soon divide, thus 
producing the tetrads. The first spindle disappears before the second 
two are formed. The suspensor consists of only two cells. 
Embryo of Indian Corn.| — Mr. W. W. Bowlee and Mr. M. W. 
Doherty thus describe the peculiarities of the structure of the embryo of 
* Bot. Centralbl., lxxv. (1898) pp. 257-61. 
t Proc. Amer. Ass. Ad. Sci., 1897 (1898) p. 275. 
j Bull. Torrey Bot. Club, xxv. (1898) pp. 311-5 (1 pi.). 
