1921] WALKER—GAMETOPHYTES OF EQUISETUM 381 
Each gametophyte consists of a flat circular disk (shown entire 
in fig. 6, which is a ventral view, and in section in figs. 8 and 9) 
of large-celled compact tissue 1-10 mm. in diameter and bearing 
many upright green branches on its upper surface. It is usually 
indented deeply at one side (figs. 1, 5, 6) and may be more or less 
lobed at the periphery, where it is surrounded by a heavy band of 
meristem (figs. 6, 8, 9) so long as growth continues. This meristem 
is often more active at some points than at others, which causes the 
marginal lobing. Fig. 6 shows the under side of the gametophyte 
whose upper surface is shown in fig. 1. The thallus was killed and 
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tissues cat’ away at A; ‘section of sporophyte shown in fig. 11; X10 
Cleared in glycerine and then photographed from below to show the 
meristem band about the periphery and the slight lobing often 
present. It is this peripheral meristem that continues the growth 
of the thallus and gives rise to the upright branches and the sex 
organs. Fig. 8 shows this meristem at each end of the section 
producing archegonia. Fig. 9 shows the same structure, but at the 
left the meristem band contains two antheridia, and at the right a 
sporophyte with foot, root, stem, and leaves differentiated. The 
entire upper surface of the thallus is covered by the upright green 
branches. These branch more or less above and are wider at the 
tip than at the base (fig. 8). Very little chlorophyll is present in the 
