PH OPHYCEA 91 
similar habit of growth. Irregularly globular and 
half-globular, corrugated forms of thallus with 
hollow interior, like Leathesia, occur, and consist at the 
most of vertical or oblique cell-rows, more or less 
Fia. 21.—Leathesia digurmis. u, plurilocular, and 6, unilocular sporangia. 
Highly magnified. 
branched, almost colourless within and giving rise 
externally to the characteristic assimilative filaments. 
In Myrionema, Microspongium, and allied genera, the 
assimilative filaments spring from a basal cushion of 
one or two layers of parenchymatous cells, or even of 
