Notes . 
273 
an upper zone of chlorophyll-bearing tissue, containing numerous 
air-spaces and traversed by the passages leading down to the antheri- 
dial cavities; (2) a middle zone of compact tissue, in which are 
embedded the antheridia, and which consists of large colourless cells, 
including scattered mucilage-sacs ; (3) a lower zone continuous with 
Fig. 17. — I. Longitudinal section through anterior end of thallus, with a male 
receptacle ; x 20. The antheridial cavities are deeply shaded ; Sc., ventral scales. 
II. Part of the same section, x 200, showing on the left the upper portion of an 
antheridium and its cavity, on the right an air-chamber, opening by a ‘ barrel- 
shaped’ pore. III. Surface-view of part of receptacle, showing two pores; the 
upper opens into an antheridial cavity, the lower into an air-chamber. 
the midrib of the thallus and consisting of compact tissue, traversed 
by strings of mucilage-cells, and bearing the rhizoids and ventral 
scales beneath. 
From these structural features it is clear that the male receptacle 
T 
