342 
F. Cavers. 
These middle lobes usually remain small, but in some species they 
grow into conspicuous appendages, often toothed, which serve to 
retain water by capillarity and also to increase the assimilating 
surface of the plant. The same purpose is served by the leaf-like 
outgrowths on the upper side of the thallus in some species ; in 
A. fusiforrnis these are lamellae of varying sizes and shapes, while in 
A. arachnoides the whole plant is covered with hair-like or plate¬ 
like outgrowths forming an irregular network of shallow water¬ 
holding chambers. In A. giganteus the thallus is sharply divided 
into a massive midrib and one-layered wings, the lobes of the 
latter being folded over towards the underside and forming hood¬ 
like water-cavities. 
Many species of Antlioceros, especially those which grow in 
dry situations, have perennating tubers in which food is stored 
and which persist after the rest of the plant has died down. In 
most cases these tubers arise on the edge of the thallus, probably 
always from a growing-point, and either remain as swollen bodies 
slightly buried in the soil, or they may become stalked and pushed 
well below the surface. Examples of tuber-bearing species have 
been figured by Howe (14) and by Goebel (9); as was shown by 
Ashworth (1), the tuber has a firm envelope of corky cells, while 
the inner cells contain proteid-grains and oil-drops. 
The tissues of the thallus are usually almost uniform, though 
the central cells are often, especially in the older parts of the thallus, 
greatly elongated and have their walls reticulately thickened. 
Though not forming a very definite strand, these cells may perhaps 
be compared with the pitted cells forming the conducting tissue in 
such Liverworts as Pallavicinia, but it must be remembered that 
similarly thickened cells often occur in the Marchantiales. In 
several species of Antlioceros there occur cavities of irregular shape 
and size, which are formed by splitting apart of the cells and 
contain abundant mucilage. In A. dichotomies, of which the writer 
has examined abundant fresh material, these mucilage sacs are 
sometimes inhabited by Nostoc, the chains of this alga having 
apparently entered the otherwise quite closed sacs by way of 
the intercellular spaces; in some cases the Nostoc chains were 
seen to be connected with the normal Nostoc- cavities which at 
first open by a stoma-like slit on the underside of the thallus. 
The Antlioceros thallus does not bear the special gum-forming 
hairs which are so common in Liverworts, but the special mucilage- 
slits, to be described presently, keep the growing-point bathed in 
