95 
Biology of Fegatella conic a. 
are kept dry, and (2) the fully developed rhizoids can be shown by plasma- 
lysis to have entirely lost their protoplasmic contents, whilst in younger ones 
the protoplasm is only found at the extreme apex, where tubercles are 
absent and where the absorption of liquids is shown by experiment to be 
most active. Kamerling demonstrated the existence of negative pressure in 
the rhizoids, by placing on a razor a drop of water which contained carmine- 
powder in suspension, cutting through a bundle of rhizoids, keeping the 
cut ends in the liquid for a few seconds, and then spreading out the upper 
part of the bundle (i. e. that attached to the thallus) on a slide and 
examining the rhizoids under the microscope. In the case of the plain 
rhizoids, the negative pressure is very marked, the liquids passing in for a 
distance of several millimetres, but in the tuberculate rhizoids the carmine 
particles are arrested by the tubercles immediately beyond the cut end. 
As already stated, the tuberculate rhizoids spring from the angles 
between the ventral scales and the surface of the midrib, the scales 
evidently serving to protect the rhizoids against evaporation and mechanical 
injury, besides forming narrow spaces in which water is retained by 
capillarity. The apical appendage of each scale, after it has fulfilled its 
function of protecting the growing-point of the thallus, becomes, in con- 
sequence of the active growth of the latter, thrust on to the ventral surface 
and then soon withers. The basal portion of the scale, however, persists 
and covers the ventral groove in which lie the bundles of tuberculate 
rhizoids (Pl. VI, Fig. 17). 
In the submerged aquatic form of Fegatella , a few rhizoids are borne in 
the axils of the reduced ventral scales, but though these rhizoids correspond 
in position with the tuberculate ones of terrestrial plants, the tubercles are 
almost entirely wanting. This observation lends support to the view that 
the tuberculate rhizoids are adapted for the storage of water, whilst the 
plain rhizoids serve to conduct water and to attach the thallus to the 
substratum. 
Mycorhiza. 
The thallus of Fegatella is frequently infested by the hyphae of a 
Fungus, regarded by Beauverie (1902) as a Fusarium. These hyphae 
are usually confined to a zone of cells underlying the air-chambers in the 
midrib, but are sometimes found also in the compact tissue of the lamina 
on either side (PI. VI, Fig. 22). They penetrate the cell-walls and often 
become branched and coiled up within the cells, bearing here and there 
swollen vesicles, which may be either terminal or intercalary in position, 
and in the latter case are often arranged in chains (PI. VI, Figs. 23, 24, Ves). 
The writer has found that these vesicles are of two kinds. Those formed 
during summer are thin-walled, usually aggregated in chains, and some- 
times become ruptured, so that the cells of the thallus become filled with 
