Pollen Mother-cells of Certain Plants. 51 
apparent then that this period is most favourable for any interchange of 
discrete particles, or even for chemical influence. 
According to some authors 1 the two filaments of each pair in the 
spirem fuse by means of their linin substratum, and an interchange of 
particles according to Allen and Strasburger could probably occur. If such 
an interchange does occur, it must take place in the spirem according to my 
observations. Berghs (’04, ’05) and Gregoire (’04, ’07) maintain that no 
such fusion occurs. £ Ces filaments demeurent, dans chaque paire, parfaite- 
ment distincts l’un de l’autre,’ but they remain as distinct ‘ que le seraient 
deux doigts de la main entrelaces Tun autour de l’autre.’ The persistent 
duality of the spirem has also been admitted by several other investigators, 2 but 
these authors have figured the two univalent portions most closely associated 
during the spirem stage, thus perhaps admitting of a possible symmixis. 
Absence of a Continuous Chromatic Spirem. 
Many authors have recently come to the conclusion that a continuous 
chromatic spirem does not exist. Strasburger (’05) was unable to find such 
a spirem in the somatic cell of Funkia and Galtonia. Gregoire and his 
students are also of the opinion that such a spirem is not present in vegeta- 
tive and germ nuclei. Although a continuous spirem is found in Podo- 
phyllum peltatum, Campanula grandis, and Helleborus foetidus , I was unable 
to find one in Calycanthus floridus and Thalictrum purpurascens. My latest 
studies confirm my former observations on these two plants. Richardia 
africana , however, forms an apparently continuous chromatic spirem. In 
such cases as Richardia, Allium, &c., in which there is an apparent con- 
tinuous chromatic spirem, there probably exist individual segments or 
chromosomes very closely united, without any very extensive linin intervals 
as described for Thalictrum and Calycanthus. Gregoire (’07) has shown 
that the individual chromosomes of the spirem converge toward a definite 
point in Osmunda , much as has been described for many animal cells, so 
that the absence of a continuous spirem seems out of the question in this 
plant. 
Second Contraction Figure. 
The second contraction figure, in which the chromosomes are arranged 
in a more or less regular fashion about a central point, 3 has been nowhere 
observed in these plants, and cannot be held to be characteristic of maturation 
divisions in general, although it may occur in some plants. Gregoire (’07) 
1 Allen (’04, ’05), Strasburger (’05), and Lagerberg (’05). 
2 Overton (’05), Cardiff (’06), Marechal (’04, ’05, ’07), Bonnevie (’05), Gregoire and Deton (’06), 
and Schleip (’06). 
3 This has been described as a second synaptic contraction by some authors. Compare 
Miss Sargant (’96, ’97), Tretjakoff (’04), Farmer and Moore (’05), Allen (’05), Overton (’05), 
Schaffner (’06), Mottier (’05, ’07), Griggs (’06), Gregoire (’07). 
E 2 
