M archantiales. 
109 
and the form of the involucre depends merely upon the amount of 
the surrounding tissue which grows out and the rate at which it 
grows forward over or around the group of archegonia. Thus there 
is no real difficulty in homologising the involucre of Monoclea with 
Monoclea Fovstevi. 
Fig. 16. A.—Part of a vertical longitudinal section of a male plant, 
traversing a receptacle. The walls of the antheridial cavities bear numerous 
club-shaped mucilage-hairs, and much larger hairs are borne at the anterior 
end of the of the receptacle, on the right. On the left are shown five of the 
wide rhizoids which grow downwards ; on the right, six of the narrow rhizoids 
which grow back parallel with the lower surface of the thallus. x20. B.— 
Part of a similar section, showing the growing-point of the receptacle, with 
the large mucilage-hairs and several developing antheridia. x90. C.—Part 
of a vertical longitudinal section of a female plant, traversing a receptacle. 
Between the archegonia arise numerous long mucilage-hairs ; rhizoids as in A. 
x 35. D.—Part of a similar section, showing a fertilised archegonium containing 
an embryo, and on the left of this an unfertilised archegonium. x90. 
that of the Corsiniaceas and Targioniaceas. The three families 
stand apart from the Ricciaceas on one hand and the Marchantiaceae 
on the other with regard to the arrangements for the protection of 
