Geothallus tuberosus, Campbell. 499 
tozoids (Fig. 20) are extremely small, and show about two 
coils. The tapering forward end is provided with the usual 
two cilia, which are almost equal in length to the body of 
the spermatozoid. 
The stalk of the antheridium is derived from the second 
of the three primary cells into which the mother-cell is 
divided. This cell is often divided by cross-walls, so that the 
stalk is composed of four short rows of cells ; but quite as 
often the second vertical division is suppressed, and it is then 
made of but three (Fig. 15, a). The transverse divisions are 
never numerous, and the pedicel remains short. In the 
formation of longitudinal walls in the pedicel Geothallus 
differs from Sphaerocarpus , where the pedicel always is 
composed of but a single row of cells, and resembles much 
more Fossombronia or Pallavicinia 1 , where there are also 
found quadrant-walls in the body of the antheridium. At 
maturity it is usually somewhat oblique, being bent forward 
more or less. 
Each antheridium is surrounded by an envelope, closely 
resembling that found in Sphaerocarpus , and formed in exactly 
the same way. Almost simultaneously with the first division 
in the antheridium mother-cell, the superficial cells immediately 
begin to grow out about it in the form of a ring-shaped wall, 
and very soon outstrip the antheridium, which is sunk in 
the involucre thus formed. The wall of the involucre remains 
but one cell thick, except at the extreme lower part where 
it joins the thallus. The upper part of the envelope is pro- 
longed into a neck, through which the spermatozoids are 
discharged. The enlarged lower part fits closely over the 
antheridium (Fig. 19). 
Sometimes the antheridia are produced only in small 
numbers, and may form a single row occupying the median 
line of the shoot ; but usually they are produced in larger 
numbers, and may almost completely cover the dorsal surface 
of the thallus (Fig. 10), much as in Sphaerocarpus . 
1 Leitgeb, 1. c., iii. p. 88. 
