1918] HAUPT—PALLAVICINIA 525 
series were made by Dr. LAND and Mr. Mason, while those showing 
the development of the archegonium and the sporophyte were pre- 
pared by the writer. 
Thallus 
The vegetative body of Pallavicinia Lyellii consists of a creep- 
ing, prostrate thallus 4-5 mm. wide, composed of a midrib with thin, 
one-layered, lateral wings, and bearing rhizoids. The margin is 
somewhat undulate, with no indications of hooked appendages as 
in P. longispina, P. xiphioides, or P. Zollengeri. The midrib con- 
sists of pitted conducting cells with thickened walls, which become 
differentiated directly behind the apical cell (fig. 45); about 70 to 80 
may be seen in cross-section (fig. 44). ANSLEY and CHIcK (15) 
made a careful study of these cells and showed by eosin solutions 
that they conduct water. Miss McCormick (8) demonstrated that 
in Symphyogyna aspera they are composed of pectose. These con- 
ducting cells are also found in Hymenophyton. 
Growth of the thallus is by means of a dolabrate (zweischneidig) 
apical cell (fig. 43). This feature seems to have first been observed 
by LerrcEs (7), who discusses at considerable length apical growth 
and the development of the thallus body. Two-celled mucilage 
hairs arise both dorsally and ventrally in connection with the apical 
cell, strongly resembling sex organ initials. 
Branching is of two kinds: apical, from the apical cell; and 
endogenous, from ventral adventitious shoots. Material showing 
the origin of the latter was lacking and hence LeITcEB’s statement, 
that the conducting tissue of the ventral branch is not continuous 
in origin with the central cells of the main thallus, could not be 
verified. 
Sex organs 
The gametophytes of Pallavicinia Lyellii are strictly dioecious, 
the male plants being slightly more slender than the female. Both 
antheridia and archegonia are dorsal, the former lying in 2 parallel 
rows on each side of the midrib, and the latter remaining directly 
above the midrib, slightly raised on a pad. Two involucres are 
present, the outer one corresponding to that of Symphyogyna and 
Monoclea; the inner one, or perianth, is characteristic of Pallavi- 
cinia, Podomitrium, and Calycularia. 
