294 Sir as burger.- —The Periodic Reduction of 
nucleus of the mother-cell as it leaves the resting stage takes 
place just as directly as in the pollen-mother-cells of the 
Phanerogams. It can be easily ascertained that this number 
persists through the two divisions which result in the 
formation of the four spores. On the other hand, the nuclei 
of the archesporial cells, previously to the differentiation of 
the spore-mother-cells, contain a larger number, probably 
twice as many or nearly so. This higher number persists, 
after the differentiation of the spore-mother-cells, in the 
external tissues of the sporangium. This is shown in the 
figures published by Dr. J. E. Humphrey 1 , who investigated 
the nuclei of Osmunda , with regard to the behaviour of their 
centrosomes and nuclei, in my Botanical Laboratory last 
winter. Thus his Fig. n shows a mother-cell of Osmunda 
regalis undergoing the first division, and Fig. 1 2 a mother-cell 
undergoing the second division ; whilst Fig. io also shows the 
division of a tapetal mother-cell. Prothallia, developing from 
spores sown in a culture-solution, showed twelve chromosomes 
in all stages, that is, the same number as in the spore-mother- 
cells. The search for nuclear divisions in developing prothallia 
requires a great deal of patience, for, so far as my experience 
goes, they do not take place at any particular time of the day, 
and hence they are only to be found in isolated cases. My 
attempts to arrest the nuclear divisions by exposure to low 
temperatures, or by absence of light, so that they might take 
place more frequently at appropriate times, led to no result : 
influences which had proved to be effectual in Spirogyra had 
in this case no effect. All that I could do was to examine 
a very large number of prothallia which had been fixed in 
alcohol at various times of the day, and had been stained. 
I was successful in carrying the counting of the chromosomes 
up to the commencing development of the antheridia and 
spermatozoids, and in all cases I found the number to be the 
same. It is unnecessary to say more than that the processes 
1 Berieht. d. deutsch. bot. Ges., 1894, 5 > Taf. VI: see Notes, this 
number. 
