112 Rhodora [May 



In the account just given of P. platyphylla the history of P. platy- 

 ■phylloidea is Hkewise briefly treated. When Schiflfner proposed 

 M. Jackii as a new species he stated that it differed from M. platy- 

 phyUoidea in its simply pinnate shoots and slightly larger cells, the 

 North American species being described as closely bipinnate. Miiller 

 considers these differences of but slight importance and was, more- 

 over, unable to confirm them in his study of authentic specimens of 

 the two species in question. He therefore reduced M. Jackii to 

 sjTionymy and the writer, from a study of European specimens cited 

 by Miiller, sees ever\' reason for following his example. 



In P. platyphylloidea, according to Miiller's accounts, the plants 

 are somewhat more robust than in M. platyphylla, and the secondary 

 stems are usually only once-pinnate with branches of variable length, 

 the shoot-system thus acquiring an irregular contour; the lobes of the 

 leaves are closely imbricated and suborbicular (usually as broad as 

 long or even broader), the base being crispate and auriculate, the apex 

 broadly revolute, and the margin practically entire; the lobules are 

 about twice as wide as the stem, broadly ovate, broadly rounded at 

 the apex, shortly or not at all decurrent, and slightly revolute along 

 the margin; the leaf -cells average 25 ju in diameter in the middle of 

 the lobe, and the development of the trigones varies according to 

 the environment; the underleaves are of about the same width as 

 the lobules, their outline is suborbicular, and they are shortly decur- 

 rent on both sides, the decurrent portions sometimes bearing a few 

 small and scattered teeth, while the rest of the margin is entire and 

 sometimes revolute; the perichaetial bracts, which are reduced to a 

 single pair as in P. platyphylla, are smaller than the leaves, the lobe is 

 elongated-ovate and entire, ami the lobule is only one-third as large 

 as the lobe, ovate in form, rounded at the apex, and entire, or indis- 

 tinctly dentate; the perichaetial bracteole in broadly oval, entire or 

 sparingly toothed in the basal region; the perianth is ovate in outline, 

 narrowed toward the two-lipped mouth and shortly dentate or (in 

 Schiffner's words) densel\- ciliated with cilia one to five cells long. 

 The capsules split as in P. platyphylla and the spores average about 

 46 /x (according to Schiffner) ; the elaters are mostly 9-10 fx in diameter 

 and usually show a single spiral band throughout their length; in 

 some cases two spiral bands are present in the middle of the elater 

 but only one extends to each end. 



Since P. platyphyUoidea is the commonest species of Porella in 



