Meiotic Mitoses of Osmunda. 137 
This investigation includes several species of Osmunda which have been 
severally minutely examined. The greater number of the drawings have 
been made from the nuclei of 0. palustris var. aurea , but nuclei of other 
species have been intercalated when they showed any one particular phase 
more clearly. The plates therefore comprise figures of O. palustris , O. palus- 
tris var. aurea , 0. palustris var. undulata , and 0. regalis. 
The plants have been most successfully grown in greenhouses at the 
Chelsea Physic Garden under the personal care of Mr. Hales, the Curator, 
to whom I am greatly obliged. 
The following nomenclature will be adopted throughout the paper : 
The term ‘ thread ’ will be used to specify the longitudinal half of an 
entire univalent spireme or chromosome which first appears during telo- 
phase. The two £ threads ’ or halves separate during telophase, and reasso- 
ciate during the ensuing prophase, forming an entire univalent spireme or 
‘ filament’ which eventually becomes an entire univalent chromosome. The 
term ‘ filament ’ will be used to specify the entire univalent spireme, the 
product of the close lateral association of two threads (i.e. of two longitu- 
dinal halves of univalent spireme). The term c strands * will be used to 
describe the very fine strands of linin that connect the several chromosome 
segments of early telophase, also those which serve as fine transverse 
Connexions between the individuals of a pair of associating and dissociating 
threads, and between the individuals of a pair of conjoining and disjoining 
filaments. 
The terms ‘ association ’ or f approximation • will be confined exclusively 
to the coming together, laterally, in pairs of the ‘ threads ’ (i.e. of the two 
longitudinal halves of the univalent spireme) to form the entire univalent 
spireme, which becomes the entire univalent chromosome ; the terms ‘ con * 
junction ’ or ‘ conjoining ’ to the coming together in pairs of the ‘ filaments’ 
(i. e. of the two entire univalent spiremes) to form the bivalent spireme which 
becomes the bivalent chromosome. 
The terms ‘ fission * or ‘ dissociation ’ will be restricted to the longitudinal 
splitting of the ‘ filament ’ (he. of the entire univalent spireme) into ‘ threads ’ 
(i.e. into half univalent spiremes) and to the splitting of the entire univalent 
chromosome into daughter chromosomes ; the term 5 disjunction ’ or ‘ disjoin - 
ing ’ to the separation of the two conjoined ‘ filaments ’ (i. e. to the separation 
of the bivalent spireme into two entire univalent spiremes) and to the 
separation of the bivalent chromosome into the two entire univalent 
chromosomes. 
Archesporial Divisions. 
Probably all cytologists are agreed that the constitution of each indi- 
vidual chromosome is one of duality, and that this dominating feature usually 
persists throughout the cycles of chromosome construction and dissolution 
M 3 
