4 Rhodora [JANUARY 
From all the segregate-genera Ammodenia is supposed to be sepa- 
rated by the highly developed glandular-lobed disk, by its bladdery 
capsule and by the few pyriform seeds with nearly basal hilum, and, 
of course, by its succulent stems. Yet Pax correctly states that 
Merckia has the habit of this plant, Pax separating Merckia because — 
it has the ovary and fruit “mehr oder weniger vollkommen 3-5 
ficherig”’ and because of its obsolete disk. Ammodenia is left by 
Pax in Alsine or Minuartia, a genus distinguished by 1-celled ovary 
and the entire valves of the capsule, and he states under Merckia 
that that monotypic genus perhaps belongs also with Alsine. Never- 
theless, Ammodenia, as already pointed out by Asa Gray, has the 
ovary “more or less completely three-five-celled, the dissepiments 
soon breaking away from the walls and adhering to the more persistent 
columella;”! i. e., the supposed ovary-difference between Ammodenia 
and Merckia is not constant. Furthermore, the seed of Merckia is 
exactly intermediate in outline between the seed of Ammodenia and 
the most typical seeds of Arenaria and Minuartia, i. e., it is suborbicu- 
lar to obovate-orbicular, with the hilum nearly basal. The develop- 
ment or obsolescence of the stamineal disk is certainly not constant 
in the group, for, although Merckia physodes as a species is readily 
distinguished from Ammodenia peploides by its obscure disk, it should 
be noted that some species referred to true Arenaria and to Minuarha 
(Alsine) have highly developed disks, while the disk of Mochringa 
is well developed. The American Arenaria macradenia Wats., for 
example, is the best kind of Arenaria in its cespitose habit, acicular | 
leaves, terminal inflorescence, capsule and seeds, but its Stamineal 
disk and glands are quite as conspicuous as in Ammodenia. Ammo- 
denia is supposed to be distinguished from Arenaria, furthermore, 
by its few obovoid seeds in contrast with the many reniform seeds 
of the latter genus; yet Arenaria Hookeri Nutt., a ch 
cespitose species with acicular leaves and terminal cymes, has but 
3 seeds to a capsule, these obovoid and with a basal hilum as ” 
Ammodenia. : 
Moehringia is distinguished by its habit, well-developed disk; 
1-celled ovary, capsule-valves as in Arenaria, and reniform, lustrous, 
_ strophiolate seeds. But as already pointed out Moehringia is exactly 
simulated by species of Arenaria which differ merely in having the 
1 Gray, Gen, ii. 31 (1849). 
