314 Strasburger . — The Periodic Reduction of 
certain conjugate Algae. Klebahn 1 found that, in the ger- 
minating zygotes of Closterium and Cosmarium , the nucleus 
divides twice in rapid succession ; but the zygote then divides 
into only two cells, and only one nucleus for each of these 
two persists. Similarly, according to Chmielewsky 2 , the 
nucleus of the zygote of Spirogyra divides into four, but the 
unicellular embryo subsequently possesses but a single nucleus. 
Klebahn has already suggested that, in these cases, a reduction 
in the number of the elements, probably by fusion with 
one another, must necessarily take place 3 : and Chmielewsky 
compares the phenomena in Spirogyra with the formation of 
polar bodies, a comparison to which Klebahn offers some 
objections 4 , since the assumption of the formation of polar 
bodies after a sexual act would involve a modification of 
prevalent views as to the nature of these structures. Oscar 
Hertwig 5 considers £ that the processes described by Klebahn 
in the zygotes of Desmids, have the same object as the re- 
ducing divisions during the maturation of ova and spermatozoa.’ 
‘As in that case the double division of the nucleus involves 
a reduction by half of the normal nuclear substance, before 
fertilization, and thus prevents an accumulation of nuclear 
substance which would otherwise take place as a consequence 
of the fusion of two nuclei in the sexual act ; so, in the 
Desmids, it would appear as if it were only after conjugation 
that a reduction of the nuclear substance is eventually effected, 
and thus the doubled mass of the nucleus in consequence of 
the fusion of two complete nuclei were brought back to the 
normal. The nucleus of the zygote, instead of dividing once, 
is divided into four by two immediately successive divisions ; 
1 Studien iib. Zygoten : I, Die Keimung von Closterium und Cosmarium , 
Jahrb. f. wiss. Bot., XXII, p. 415, 1891. 
2 The paper is in Russian, but a full abstract of it is given in Famintzin’s 
Uebersicht der Leistungen auf dem Gebiete der Botanik in Russland wahrend des 
Jahres 1890, p. 16. 
3 Loc. cit., p. 441. 
4 Studien iib. Zygoten : II, Die Befruchtung von Oedogonium Boscii, Jahrb. 
f. wiss. Bot., XXIV, p. 257. 1892. 
5 Die Zelle und das Gewebe, 1893, p. 225. 
