290 
Lang . — The Prothallus 
while in Fig. 26 the section is in the median plane of the shoot, 
but at right angles to the median plane of the root. The two 
sections are thus in planes at right angles to one another. 
The superficial layer 1 of the foot was characterized by the 
dense protoplasmic contents of its cells. The extent of this 
layer, which is possibly concerned in the absorption of organic 
substances from the prothallus, is indicated by the shading in 
Figs. 25 and 26 ; a small portion of a similar section is repre- 
sented in detail in Fig. 27. These figures and Fig. 28 also 
show the irregularity of outline of the foot and the thickness 
of the outer walls of its limiting layer of cells ; these outer 
walls stained very deeply with Bismarck-brown. 
The structure of the region of attachment to the prothallus 
of the older plant shown in Fig. 23 is drawn in detail in 
Fig. 28. It was ascertained on comparing this section, which 
is approximately median as regards both shoot and root, with 
the rest of the series that the vascular system does not extend 
into the foot ; the central cells of the latter, however, seem 
to be arranged so as to facilitate the conduction of absorbed 
substances towards the vascular strand. The absorbent layer, 
though still recognizable, did not present the characteristic 
appearance seen in the younger plant (Fig. 27). This may be 
associated with the fact that the plant at the latter stage was 
devoid of chlorophyll and wholly dependent on the prothallus, 
whereas the absorbent function of the foot would be of 
secondary importance in the case of a plant with a shoot- 
system capable of assimilation. It may be noted that in the 
specimen represented in Fig. 28 the structure of the foot is 
not uniform, the region just below the insertion of the root 
being composed of smaller, thinner-walled cells with more 
abundant contents ; whether this difference possesses any 
significance is however uncertain. 
The large foot persists for a considerable time after the 
prothallus has disap peared, and wasrecognizable in much 
1 Bruchmann (loc. cit., 1898, p. 44) ascribes to this peripheral layer of the foot 
the main part in the growth of the latter; the arrangement of the cells in my 
specimens did not however seem to support such an interpretation. 
