47 
Pollen Mother-cells of Certain Plants. 
Brachystola, of Blackman (’ 03 , * 05 ) on Scolopendra , and of Downing (’ 05 ) 
on Hydra agree. Dublin (’ 05 ) holds that in Pedicellina the chromosomes 
unite in pairs during the anaphases of the last spermatogonial division. 
Ancel (’02) and Miss Stevens (’ 03 ) find in Helix and Sagitta that the 
chromosomes are united in parallel pairs in the spermatogonia. 
I desire also in this connexion to call attention to the fact that not 
only in somatic cells, but also in all the pollen mother-cells of the 
dicotyledons investigated by me in my former study, I was able to dis- 
tinguish paired elements in all the pre-synaptic nuclei. In such plants as 
Helleborus , Podophyllum and Campanula , in which an apparent continuous 
chromatic post-synaptic spirem is found, and in which the individual 
limits of the post-synaptic chromosomes cannot be distinguished, the 
paired condition in the very youngest pre-synaptic nuclei is evident. See 
Figs. 25-37, 39 and 40, 53 and 54, Pls.VI and VII, of my 1905 communication. 
These observations convinced me that the chromosomes of the penultimate 
meiotic cells appear in the mother-cell nuclei in homologous pairs. 
In order to emphasize the conception that the homologous chromo- 
somes are already paired when they enter the mother-cell, the reader is 
referred to Figs. 2 and 3, PL I, which represent exceedingly young nuclei 
of Thalictrum. In these nuclei the prochromosomes as well as the linin 
intervals are unquestionably paired. That they remain so until synapsis or 
later is shown in Figs. 4-12, PI. I. In Figs. 1, 2, and 3, PI. II, the paired 
pre-synaptic elements are quite distinct in the cells of Calycanthus. Although 
this pre-synaptic pairing is less distinct in Richardia , yet Figs. 2 and 3, 
PL III, show that this condition exists in this plant. 
It appears from my observation that this association of parental 
chromosomes in pairs occurs much sooner even than in the immediately 
preceding pre-meiotic cells. I have always observed the prochromosomes 
in pairs in all of the cells of the anther, as well as in all other somatic cells. 
It is highly probable that this association occurs during fertilization, 
and that the actual conjugation occurs during synapsis or associated 
stages. 
That the association of parental nuclear parts may occur during the 
pre-synaptic stages is further shown by the recent observations of many 
students, especially among botanists, 1 many of whom present evidence to 
show that conjugation occurs by a side-to-side union of the pre-synaptic 
chromosomes. Differences, however, exist as to the exact period, when 
this union occurs. Allen (’ 04 , ’ 05 ) finds the pairing beginning before 
synapsis, but fusion occurs in synapsis. My own account in ’ 05 2 is 
1 Gregoire (’04), Berghs (’04, ’05), Allen (’04, ’05), Rosenberg (’05, ’07), Kirkwood (’07), 
Strasburger (’05), Miyake (’05), Overton (’05), Tischler (’06), Lagerberg (’06), Noren (’07), and 
Yamanouchi (’08). 
2 See also Cardiff’s (’06), Lagerberg’s (’06), Noren’s (’07), and Yamanouchi’s (’08) results. 
