EQUTSETINEM. 
portion of each protuberance rematns slender, and forms the pedicel of the hex- 
agonal peltate scale. The outer surface of these scales is tangential to the axis 
of the spike ; on its inner side, facing the axis, arise the sporangia, five or ten in 
number on each scale. In the early stages of development each single sporangium 
has the appearance of a small blunt multicellular wart; [an axial row of the cells 
grows more vigorously than the rest, and it is the terminal hypodermal cell of 
this row which constitutes the archesporium. 
The epidermal layer divides by walls parallel to 
the surface, so that four layers of cells invest the 
archesporium, of which the two outer form the 
wall of the sporangium, and the two inner the 
tapetum]. By repeated divisions the archesporial 
cell produces the spore-mother-cells which be- 
come isolated, while of the exterior cell-layers 
which at first envelope them only the outermost 
finally remains as the wall of the sporangium. 
The mother-cells of the spores, connected to- 
gether in groups of fours or eights, float freely 
in a fluid which fills the sporangium and is inter- 
spersed with granules. The processes that take 
place in the mother-cells up to the time of the 
formation of the spores have already been de- 
scribed in detail in Chap. I (see Fig. 10, p. 14)^ 
It was there shown how the division into four 
of the mother-cells is preceded by an indication 
of a division into two, in a manner analogous 
to the corresponding process in Ferns. The 
ripe sporangium opens by a longitudinal slit 
on the side which faces the pedicel of the peltate 
scale. The very thin-walled cells of the wall 
have previously formed spiral thickening ridges 
on the dorsal, annular ones on the ventral side 
of the sporangium, arising, according to Duval- 
Jouve, in the case of E. limosum, with extra- 
ordinary rapidity immediately before the de- 
hiscence. The development of the spores of 
Equisetum, after they have made their appearance as naked primordial cells by 
the division into four of their mother-cells, shows the peculiarity of a successive 
formation of distinct coats. Each spore forms first of all an outer non-cuticularised 
coat capable of swelling, which, splitting subsequently into two spiral bands, forms 
the so-called elalers, a second and third coat soon afterwards making their appear- 
ance within it. All three lie at first closely one upon another like successive layers 
of a single coat; but when the spore is placed in water, the outer one, even at 
this period, swells up strongly and becomes detached from the others (Fig. 286, 
Fig. 285. — Eguzsett{7n Tehuateia; A upper part of 
a fertile stem with the lower half of the spike (natural 
size), b leaf-sheath, a the annular 'bract,' a: the pedi- 
cels of peltate scales which have been cut off, y 
transverse section of the rachis of the spike ; B 
peltate scales in various positions (slightly magni- 
fied) ; St the pedicel, s the peltate scale, sg the spo- 
rangia. 
* [On the development of the spores see Strasburger, Zellbildung und Zelltheilung, 3rd ed., p, 155,] 
D d 2 
