On Spore Formation and Nuclear Division in 
Mnium hornum. 
BY 
MALCOLM WILSON, B.Sc., A.R.C.S. 
Demonstrator in Botany, Royal College of Science , London. 
With Plates X and XI. 
T the present time the Meiotic Phase has been described in almost 
ff\. all the larger groups of plants, but the Muscineae form a notable 
exception to this statement. Although the reduction divisions have been 
frequently described in the Liverworts no complete account has yet been 
given of the corresponding process in the Mosses. This, no doubt, is 
partly due to the small size of the nuclei found in this group and also to 
the difficulty experienced in finding sufficiently numerous nuclear divisions 
during the development of the spores. A short description of the Meiosis 
in Mnium hornum has already been given ( 24 ), and it is the purpose of the 
present paper to complete this account. 
Several investigators have already noted nuclear divisions in various 
mosses. Ikeno ( 18 , p. 2T9) has found that eight chromosomes appear at 
the division of the nuclei in the antheridial cells of A trichum angustatum 
and Pogonatum rhopalophorum . Holferty ( 16 ) has incidentally figured 
several nuclear divisions in the cells of the developing archegonia of 
Mnium cuspidatum, but on so small a scale that the chromosomes can- 
not be counted ; no description of these divisions is given. Gayet ( 13 , 
p. 232), in his work on the development of the archegonium in the 
Muscineae, described four chromosomes both in the spermatozoid and in 
the fertilized ovum of Fissidens incurvus , but it is very doubtful whether 
the bodies discovered were really chromosomes. Beer ( 3 , p. 166) found 
four chromosomes in the dividing spore-mother-cells of Funaria hygro - 
me trica, but stated later ( 4 , p. 278, footnote) that the number in this 
plant and in several other mosses, including Mnium hornum , was much 
greater. He also refers to the compound nucleoli in the spermatogenic 
cells of Atrichum undulatum. Dr. Arens ( 1 ) has recently published an 
account of spermatogenesis in Poly trichum juniper inum and Mnium 
[Annals of Botany, Vol. XXIII. No. LXXXIX. January, 1909.] 
