Pollen Mother -cells of Lilium canadense. 241 
tudinal splitting with the facts developed in recent experimental studies 
of hybridization, has led a number of observers to a re-examination of 
those cases in which the double splitting had been described ; and some 
of these observers have been convinced that such a double splitting actually 
does not occur. Farmer and Moore (’03), reversing their former (’95) 
views, now hold that the apparently double chromosomes appearing in 
the heterotypic mitoses in both plants and animals are formed by a 
bending upon itself in the middle of each segment of the spirem. The 
spirem splits longitudinally before segmentation, but the split becomes 
nearly or quite obscured, to reappear as a fission of the daughter chromo- 
somes during or after their separation in the metaphases. This notion, 
if correct, would bring the facts in the Seed Plants and Vertebrates more 
nearly into harmony with those commonly described for the Arthropods. 
A study of the sporogenous divisions of several species of P'erns by 
Gregory (’04) gives results similar to those of Farmer and Moore ; and 
Williams (’04), who finds chromosome reduction to occur in the formation 
of the tetraspores of Dictyota , obtains in this material further corroborative 
evidence as to the method of formation of the chromosomes. Cannon 
('03 b) has brought forward some (by no means convincing) evidence that, 
in the ancestry of the microspores of both pure and hybrid races of peas, 
the chromosomes become arranged in pairs end to end (or, in one case, 
side by side) in the anaphases of the last pre-heterotypic division. 
Montgomery (’03) has recently attempted to show that in Amphibia as 
in Arthropods there occurs a conjugation of chromosomes end to end 
in pairs, and that the heterotypic division separates the two chromosomes 
of a pair. He finds, therefore, only a single longitudinal splitting. 
Strasburger (’04) has also reversed his former opinion (’00) concerning 
a double longitudinal splitting in the prophases of the heterotypic division, 
and comes to substantially the same conclusions as Farmer and Moore. 
He finds that in the pollen mother-cells of Galtonia and Tradescantia each 
chromosome divides transversely into two segments, which are finally 
separated in the heterotypic mitosis ; from the method of their formation, 
it follows that the segments of a pair are contiguous to each other in the 
spirem before segmentation. The longitudinal split, which was visible 
in the spirem at an early stage and then disappeared, reappears in the 
metaphases and anaphases of the heterotypic division, forming the grand- 
daughter chromosomes which are to be separated in the homoeotypic 
division. Strasburger finds some evidence, in the arrangement of the 
chromosomes in the equatorial plate in the heterotypic mitosis of Tra- 
descantia , of variations in the arrangement of different pairs of daughter 
chromosomes which might result in such varying combinations of maternal 
and paternal segments as is postulated by Sutton and Boveri. Strasburger 
has also studied the stages preceding those just mentioned, and he finds 
