ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
91 
cells of a number of Dicotyledons and Monocotyledons, and agrees in 
the main facts with the results obtained by other observers. He main- 
tains that there exists a very close connection between the chromosomes 
or the chromatin-ball and the cytoplasm ; in Podophyllum very delicate 
threads of cytoplasm appear to pass through the wall of the nucleus, and 
to attach themselves to the chromatin-ball. The loose state of the ball 
described by Moore as synapsis he believes to be the result of the pro- 
cesses employed. The pollen-mother-cells are described by the author 
as being connected with one another by fine strands of protoplasm. He 
believes the reduction in the number of chromosomes before the hetero- 
type division to be an apparent reduction only. 
Herr H. O. Juel * has studied the cases (in Hemerocallis fulva ) in 
which, instead of the normal tetrads of pollen-grains, more than four 
are formed. He agrees with Strasburger in tracing this irregularity to 
the first division-process, a chromatin-body remaining attached to the 
equator in the diaster-stage, and forming later a small nucleus. These 
act as normal nuclei, form spindles, and divide. The author was unable 
to detect centrospheres in the pollen-mother-cells of Hemerocallis. Simi- 
lar irregularities also occur in the second division, resulting in the 
formation of supernumerary nuclei. 
In another paper, f Prof. E. Strasburger and Herr D. Mottier, further 
discussing the second process of division in pollen-mother-cells, abandon 
the view that a reduction-division of the chromosomes takes place in 
them similar to that which has been observed in nuclear division in 
animals. No such reduction takes place in the embryo-sac, or in the 
pollen-mother-cells (of Liliaceae) ; but an ordinary nuclear division of 
the heterotype pattern. This description includes the second division 
in the embryo-sac, by which the egg-apparatus and the upper polar 
nucleus are formed. 
Biology and Physiology of the Cell-walLt — Dr. Z. Kamerling dis- 
cusses several points connected with the structure of cell-membrane. 
He states that in various circumstances bubbles may arise within the 
uninjured cell-wall, which may contain either air or aqueous vapour ; as, 
for instance, in the cells of the annulus of the sporange of ferns. In 
almost all cases cell-walls are, when dry, impermeable to air. There 
are three classes of structures in which this impermeability is especially 
manifested : viz. in structures connected with motility, such as the 
annulus of sporanges, the capsule of Jungermanniacem, the elaters of 
Hepaticm ; in structures which absorb water very rapidly after desicca- 
tion, such as the xerophytous Marchantiaceae, the testa of many seeds, 
&c. ; and in structures which live for a long time in the dry state, such 
as Selaginella lepidophylla , the leaves of mosses, &c. Where air does 
pass through dry membranes, it is generally through small fissures. 
A striking character of cell-membrane is the resistance to moistening 
of its outer surface, often the result of a layer of wax or of granules of 
resin. The chief purpose of the formation of cork is not that it is im- 
permeable to water, but that it allows the passage of air. One impor- 
tant object in the lignification of tissues is that it permits a very great 
* Tom. cit., pp. 205-26 (3 pis.). 
t Ber. Deutsch. Bot. Gesell., xv. (1897) pp. 327-32 (1 pi.). 
x Bot. Centralbl., lxxii. (1897) pp. 49-54, 85-91. 
