93 
Biology of Fegatella conica . 
and starch-grains. On tracing the cells of a row backwards, the nucleus 
is found to be broken up and diffused in the protoplasm, whilst layers of 
deeply-staining mucilage are successively deposited on the inner surface of 
the cell-wall. The mucilage appears, therefore, to be formed from the 
protoplasm of the cell, the remains of which can for some time be seen 
occupying the centre of the cell-cavity (PI. VI, Fig. 20). 
Besides these long coherent rows of mucilage-sacs, the thallus of 
Fegatella also contains large isolated mucilage-cells, which are especially 
abundant in the lamina, in the compact tissue below the chambers ; they 
also occur abundantly in the sexual receptacles. The development of these 
isolated sacs agrees exactly with that of the constituent cells of the rows 
in the midrib. The latter, which are peculiar to Fegatella , were first 
described by Nees von Esenbeck (1838, Vol. IV, p. 188), who overlooked 
the mucilaginous contents and described the organs themselves as con- 
tinuous air-canals traversing the midrib. Goebel (1879, p. 531) was the 
first to show that these supposed air-passages were in reality mucilage- 
organs, but his account of their development does not agree with the later 
description of Prescher (1882), with which the writer’s own observations are 
entirely in accord. 
Leitgeb (1881, p. 1 6) believed that the mucilage-organs might serve 
to confer rigidity on the thallus, and Prescher was also inclined to attribute 
a purely mechanical function of this kind to these organs, but it seems more 
reasonable to accept the view, suggested by Goebel, that they act as water- 
reservoirs. The writer has found that in plants growing submerged in 
water the midrib shows no trace of mucilage-sacs. 
Ventral Scales. 
The development of the ventral scales can be readily followed by 
examining series of longitudinal sections through the growing-point. 
Immediately behind the latter, some of the ventral superficial cells grow 
outwards and forwards, dividing rapidly so as to give rise to plates which 
remain one cell thick. A superficial cell first grows out and becomes 
divided by a transverse wall ; the outer cell then grows rapidly in length, 
forming a long club-shaped mucilage-hair, which curves upwards over the 
growing-point. This hair then ceases to grow, but the cell below it divides 
actively and forms a plate, the hair being thrust on to the upper surface of 
this new outgrowth, which becomes the discoid appendage of the scale 
(PL VI, Figs. 12-15). In the meantime a zone of cells at the base of 
the appendage begins to show active growth, keeping pace for a time with the 
growth in length of the thallus and thus maintaining the position of 
the coloured scale-appendage in the notch at the apex of the thallus. The 
fully developed scale may therefore be divided into three portions, each 
representing a distinct stage in its development, viz. (x) the original 
