ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 555 
is a rotating one, tlie cilia continuing to vibrate for a considerable period 
after the rotation has ceased. 
Development of Pollen-Grains of Allium.* — M. C. Ishikawa has 
studied the development of the pollen-grains in Allium Jistulosum. On 
the first division of the pollen-mother-cells each of the eight chromosomes 
splits longitudinally, and many of the chromosomes thus formed become 
bent into a Y-shape. These gradually shorten, and unite into groups of 
four at the joints. When such a group of chromosomes assumes an 
equatorial position, the separate chromosomes of each pair are so arranged 
in the equatorial plate that one faces each pole. After nuclear division 
we have at each pole of the karyokinetic spindle eight Y-shaped daughter- 
chromosomes. Each of these daughter-chromosomes is now broken 
through at the point where the two arms meet, the mode of division being 
transverse, not longitudinal. In the first division, therefore, each pollen- 
mother-cell undergoes in succession a longitudinal and a transverse 
division, so that we get finally eight pairs of chromosomes or 16 separate 
chromosomes at each pole. Then each chromosome of the daughter- 
nuclei breaks up into microsome grains. 
The second division, which finally produces four pollen-cells, proceeds 
heterotypically. The chromosomes take the form of rings, and are eight 
in number. No longitudinal division takes place ; the nucleus of each 
pollen-cell contains eight simple chromosomes. The formation of the 
vegetative and generative nuclei in the pollen-cell is usually completed 
by each chromosome undergoing longitudinal division. 
Development of Sexual Cells in Typha.j — Mr. J. H. Schaffner has 
followed the development of the stamens and carpels in Typha latifolia. 
Notwithstanding the primitive type of flower, it presents a highly 
modified archesporial region. There is only a single archesporial cell, 
from which a single primary tapetal cell is cut off, this again dividing 
into two cells by a vertical wall. 
Polyembryony in Allium odorum.t— Herr F. Hegelmaier is able 
to confirm, in all the main points, the account given by Tretjakow § , of 
the occurrence of several embryos in the embryo-sac of Allium odorum. 
The adventitious embryos are never the result of direct impregnation by 
a pollen-tube, and may be regarded as parthenogenetic, being apparently 
due to an excitation resulting from the impregnation of the ovum-cell. 
These adventitious embryos are of 3 kinds : — (1) Derived from the egg- 
apparatus, i.e. from the abnormal development of one or both of the 
synergids. (2) Derived from the antipodals. In only one case did two 
of the antipodals develop into embryos ; never more than two. The 
author was unable to detect any predisposition in one of the antipodals 
over the others. (3) Parietal adventitious embryos, springing from the 
inner surface of the ovule at different, apparently arbitrary, spots, but 
usually at some distance from the egg-apparatus. The author was not 
successful in tracing these adventitious embryos back to the unicellular 
condition. Two may occur in the same ovule, or one accompanied by one 
of either of the other kinds. 
* Journ. Coll. Sci. Tokyo, x. (1897) 31 pp. and 2 pis. See Bot. Centralbl., Ixxi. 
(1897) p. 211. t Bot. Gazette, xxiv. (1897) pp. 93-102 (3 pis.), i 
J Bot. Ztg., lv. (1897) pp. 133-10 (1 pi ). § Cf. this Journal, 1895, p. 450. 
