36 Lang. — Prothalli of Ophioglossum pendulum 
the prothallus ; all the other walls stain blue with this reagent. 
The tissue containing the endophyte comes within these super- 
ficial layers. It is composed of parenchymatous cells, no 
marked elongation being recognizable even in the axial 
region. The cells containing the Fungus are mixed in about 
equal numbers with others similar in size and shape, which 
contain numerous starch-grains (Fig. 45). Starch is also to 
be found in cells containing the Fungus. 
It has already been mentioned that the appearance of the 
lobes of the vegetative region does not suggest their origin as 
branches referable to the apical growth. Fig. 45, which is 
a section through a young lobe of the prothallus shown in 
Fig- 38, indicates that the lobe arises by divisions taking 
place in a considerable number of cells of the outer layers. 
The tissue resulting from this generalized meristematic activity 
is at first free from the Fungus ; subsequently the latter extends 
to the central tissue of the lobe, which then presents the 
same appearance in section as the unlobed vegetative region 
(Fig. 44). 
The distribution of the endophytic Fungus has been indi- 
cated above. It remains to consider its structure and the 
changes it undergoes during the growth of the prothallus. 
In nearly every rhizoid, hyphae were seen, which presumably 
enter from the soil. In the older prothalli the rhizoids often 
break down, exposing the hyphae (Figs. 46, 47). The hyphae 
run down within the rhizoid and enter the underlying cell, 
across the cavity of which they usually pursue a straight 
course. In the outer two or three layers the filaments may 
branch and sometimes run for a short distance parallel to the 
surface, but they do not give rise to other organs as in the 
deeper tissues. In the cells of the latter, when sections 
through a young prothallus are examined, large oval or 
spherical vesicles with thin walls are found (Fig. 48). These 
may occur singly or several together, and vary in size. Oc- 
casionally their connexion with the fine hyphae entering the 
cells can be observed. The vesicles have a protoplasmic body, 
which, in some cases, completely fills them ; in most it forms 
