and Helmin thostachys zeylanica . 35 
indicate the freedom of the superficial layers of the vegetative 
region from the Fungus. 
Owing to the growth in length and formation of new sexual 
organs having ceased in almost all the available prothalli, the 
apex was somewhat difficult to investigate. It was however 
determined that growth was referable to a single apical cell ; 
in longitudinal section this appears triangular (Fig. 41), in 
cross section or in apical view it is four-sided. Thus, as was 
the case in Ophioglossum pendulum , the apical cell is here 
a four-sided pyramid. The segments, which are cut off by 
walls successively parallel to the four sides, soon divide by 
periclinal walls ; the inner cells contribute to the axial tissue, 
while the layer in which the sexual organs are formed can be 
traced to the superficial segments. 
The structure of the sexual region is most clearly shown in 
the male prothalli. Fig. 42 represents a median longitudinal 
section through this region, and Fig. 43 a transverse section. 
The uniform distribution of the antheridia round the circum- 
ference of the latter section makes the radial symmetry of the 
prothallus evident. The tissue between the antheridia shows 
indications of having arisen by periclinal divisions of superficial 
cells keeping pace with the increase in size of the antheridia. 
The central tissue consists of elongated cells, which are 
polygonal in cross section. They have thin transverse septa. 
The appearance of this tissue suggests that it is useful in the 
conduction of plastic material from the vegetative region to 
the growing-point. The structure of the short wide sexual 
region in the female prothallus is essentially similar, but the 
elongation of the central cells is less marked. 
The outer two or three layers of cells of the vegetative 
region (Fig. 44) are somewhat flattened. Here and there cells 
have grown out into rhizoids, the bases of which alone remain 
in the specimen figured. An uninjured rhizoid is shown in 
Fig. 46 ; it is unicellular, and is separated from the under- 
lying cell by a wall parallel to the surface of the prothallus. 
A cuticle, staining yellow with Schultze’s solution, is present 
on the rhizoids and extends continuously over the surface of 
D 2 
