THE MORPHOLOGY AND SYSTEMATIC POSITION OF PODOMITRIUM 201 
As in other Jungermanniales the growth of the shoot is from a 
single apical cell which closely resembles that found in most species 
of Blyttia.2 It is the common ** two-sided" apical cell, with segments 
cut off successively right and left. In horizonatal section it has the 
form of a rather narrow isosceles triangle, while in vertical longitudi- 
nal section it appears as a nearly equilateral triangle (fig. 2, A, B). 
Fig, 2, A. Vertical longitudinal section through the apex of the thallus, 
showing the single apical cell, x; X about 300. B. Horizontal section of the thallus 
apex. C. Cross-section of the thallus, showing the very unequal wings, and the 
massive midrib with its strand of conducting tissue; X about 35. D. The central 
region of the midrib; X about 200. 
In the position of the sexual organs Podomitrium most nearly re- 
sembles Metzgeria in having them borne upon special short branches 
which arise from the flanks of the midrib upon the ventral side of the 
thallus. These special fertile branches at once distinguish Podomit- 
rium from Blyttia where both archegonia and antheridia are borne 
upon the unmodified thallus. The antheridia are borne upon short 
flattened branches which may be produced on both sides of the midrib 
of a main shoot, or, in case the lamina of the latter is suppressed, on one 
- Campbell, D. H. and Williams, F. A Morphological Study of Some Member 
of the Genus Pallavicinia. Stanford University, 19 14. 
