ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
553 
pollen-grains ( L . tigrinum) show a single much-twisted ribbon with a 
row of chromatin granules on each edge. In many cases the chromatin 
granules appear to be arranged in opposite pairs. Centrospheres were 
observed in connection with both the pollen-tube nuclei and the genera- 
tive nucleus. In many cases the pollen-tube nuclei were seen to divide. 
In L. philadelpJiicum the nucleus of the archesporial cell appears 
during the first division with 12 chromosomes. At an early stage the 
linin-thread of the chromatin-network begins to thicken, and the granules 
undergo transverse fission. After division of the granules the whole 
chromatin band undergoes longitudinal splitting, and the double threads 
thus produced begin to twist upon each other. The twisted band finally 
manifests itself as a single continuous spirem, which doubles up and 
twists into twelve loops. These break apart and give rise to the twelve 
chromosomes. The two linin-threads with their granules, which com- 
pose the loop, continually become more intimately associated, so that the 
loop appears like a single linin-thread with two irregular rows of 
chromatin-granules. The chromatin-loops become shorter by contrac- 
tion, and receive a thick deposit of some substance which stains light at 
first, but later takes the same colour as the chromatin. The chromo- 
somes arrange themselves in the equatorial plane in such a manner that 
the end containing the two free ends of the original chromatin-loop is 
untwisted and finally cut in two by a transverse division. 
The nucleus has at first about three nucleoles, each with one or more 
large granular vacuoles. After the longitudinal splitting of the chro- 
matin-band, there arise in the nuclei numerous small vacuolated bodies. 
These are successively abstricted from the mother-nucleole by a process 
of budding, and give rise to numerous micronucleoles, which all pass 
out into the cytoplasm before the formation of the mother-star ; and 
later, at about the beginning of the close daughter-skeins, these micro- 
nucleoles all pass back into the daughter-nuclei, and by aggregation 
form the new nucleoles of the daughter-nuclei. This process is re- 
peated for every division of the female gametophyte. 
At about the time of the division of the chromatin-granules, there 
appear in the cytoplasm peculiar cytoplasmic threads which pass from 
one side of the cell to the other, and are mostly tangent to the nucleus. 
At a later stage, at about the beginning of the nuclear migration, these 
threads have disappeared, and numerous radiating threads pass out at 
right angles from the nuclear surface and extend to the cell-walls. 
Similar radiations appear round the daughter-nuclei; and the micro- 
nucleoles, as they are drawn into the daughter-nuclei, seem to be in 
contact with these cytoplasmic threads. 
Two centrospheres appear beside the resting nucleus, and, in the 
mother-star stage, a single centrosphere appears at each pole of the 
spindle ; while a little later, during metakinesis, a centrosphere appears 
at each point with a double centrosome. In the daughter-skein stage 
there are two centrospheres at each pole, which are often quite distinct, 
and can easily be differentiated from the micronucleoles. 
Fertilisation and Embryogeny of Triticum.*— Herr M. Koernicke 
has made a detailed examination of the processes which take place before 
* Yerhandl. Naturhist. Ver. Preussen Kheinl., liii. (1896) pp. 149-85 (1 pi. and 
3 figs.). v 
2 Q 2 
