48 ALTERNATING GENERATIONS 
latter the “haploid” phase. It happens that the facts are more readily 
observed in most Seed-Plants than in Pteridophytes, owing partly to the 
greater size of the spindles, partly to the number of the chromosomes 
being smaller than in most of the Archegoniates. Accordingly we have 
the record of the numbers from over 60 Seed-Plants, showing with remarkable 
Fic. 31. 
Successive stages of nuclear- and cell-division in an embryonic tissue. #=nucleus. 
zl=nucleolus. w=nuclear wall. c=cytoplasm. ch=chromosomes. &=polar-cap. 
s=spindle. 4o=nuclear plate. ¢=young daughter-nuclei. w=connecting threads. 
z=cell-plate. 2=new septum. In x the resting nucleus is shown. In 2 and 3 the 
segregation of the chromosomes. In 4 the chromosomes are seen with transverse discs. 
In 5 the arrangement of the chromosomes to form the nuclear plates and their longitudinal 
fission. In 3-5 the formation of the spindle from the polar-caps. In 6 the longitudinal 
fission of the chromosomes. In 7 their separation towards the poles has begun. In 8 the 
daughter-chromosomes are completely separated. In 9 they are proceeding towards 
the poles. In 10, 11, and 12 the daughter nuclei are being formed. In 9-11 the connecting 
threads and the cell-plate are being formed. In 12 the completion of the septum. 
xX about 600. (After Strasburger.) 
constancy that the number of chromosomes in the dividing nuclei of the 
sporophyte is double that in those of the gametophyte. Common numbers 
are 32:16—24:12—16:8; while they run as low as 12:6 or 6:3, and 
as high as 64:32 or 96:48. 
Records from the Gymnosperms bring evidence of the same difference 
between the two generations in various species of “mus, etc. Among 
Pteridophytes it has been observed in such Ferns as Osmunda, Alsophila, 
