114 
p- 41, t. VL, fig. 31; Ralfs in Prit. Infus., p. 894; Donkin, Brit. Diat., p. 73, pl. 
XIL., figs. 6a and 6b; Brun, Diat. Alpes and Jura, p. 73, pl. VII., fig. 12; O’Meara, 
Rep. on the Irish Diat., p. 368, pl. 31, fig. 30; Van Heurck, Syn. Diat. Belg., pl. 
XIL., fig. 18. 
Navicula gibberula, Kutz, Bacill., p. 101, t. IIL., fig. 50%; Sm., Syn., Vol. i., p. 
51, pl. XVIL., fig. 160; Ralfs in Prit. Infus., p. 895; Schumann, Diat. der Hohen 
Tatra, p. 76; Brun, Diat. Alpes and Jura, p. 73, p!. WII., fig. 11; O’Meara, Rep. 
on the Irish Diat., p. 368; Van Heurck, Syn. Diat. Belg., pl. XII., fig. 19. 
Navicula leptogongyla, Kutz., Bacill., p. 99, t. IV., fig. 9; Rabenh., Sussw. Diat., 
p- 41, t. V., fig. 8; Ralfs in Prit. Infus., p. 895. 
Valve with triundulating margin terminating in cuneate ex- 
tremities and forming three inflations, of which the central is the 
largest ; longitudinal free space narrow and slightly expanded at 
the middle ; striz fine and transverse. 
Hab.—Fresh water, frequent. (Plate LXIX., fig. 14.) 
Kiitzing seems to have relied on size and outline in separating 
NV. gibberula as a species distinct from NV. démosa.— Donkin. 
Note on the Flowers of Populus hetercphylia, L- 
‘It appears that the flowers of this poplar have never been 
fully and accurately described. Dr. Torrey, in the Flora of New 
York, remarks that he had not seen the staminate catkins, and 
there are none in his herbarium. Having recently had occasion 
to collect a large number of both kinds of catkins at the time 
when they were just mature (May 8), I made a careful examina- 
tion of them, and here place my observations on record. 
The staminate are from 5 cm. to 7 cm. long, oblong, 15 
mm. thick; they are extremely fragile, merely shaking the tree 
causing them to fall to the ground in great numbers, while a hard 
rain was noticed to have the same effect. They do not fall away 
from the branch entire under such circumstances, but break off 
at a short distance from the base; they are borne singly on wood 
of the previous year a few inches from the terminal buds of the 
present, but rarely more than two on each twig. They are com- 
posed of numerous flowers, very densely aggregated when 
young, but becoming looser in the elongation of the axis. Their 
flowers consist of an oblique disc with spreading border, some 
_what concave in the middle, which supports numerous stamens 
{in one 44 were counted); the anthers are oblong and obtuse, 
3 mm. long by I mm. broad, flat on the dorsal side and provided 
. 
