40 
EQUISETACEiEo 
Stem, with which, 
m 
characterizes E. hyemale, E. Mackaiij and the more usual forms 
of E. variegatum^ but has a smoother feel, like that of E, pa- 
lustre, the species immediately following. A transverse section 
of the stem, which is given below, also differs considerably 
from that of the usual plant, as represented by the right hand 
figure at page 30. The sheaths are scarcely larger than the 
dried specimens, they appear perfectly 
concolorous, with the exception of a 
narrow, sinuous, black band, at the sum- 
mit of each. The teeth are very short, 
somewhat wedge-shaped, generally blunt, 
and have obscure membranous margins ; 
but they are so easily injured by car- 
riage, &c., that dried specimens rarely 
exhibit them in perfection : they vary 
with striae from eight to twelve in num- 
ber. As in the usual form, the sheath 
of the catkin is much larger and looser than the rest : its 
teeth are also longer, and their membranous edges dilated and 
conspicuous. The catkin is small, black, terminal, striated and 
apiculate. 
The most striking characters whereby to distinguish the pre- 
sent from the usual form of the species, are its great size, both as 
regards height and stoutness, its erect habit, its aquatic locality, 
and the comparative smoothness of the stem. Mr. Wilson ap- 
pears to attribute the great size and erect habit to its aquatic lo- 
cality, and its greater smoothness to the combined influence of 
water and the soil of the district in which it grows ; and he ex- 
presses to me his unwillingness to admit it as a species. It may 
indeed be urged that the erect aquatic plant from Dublin and 
Kincardineshire is somew^hat intermediate ; indeed Mr. Moore, 
who insists on the distinctness of the Port Marnock and Dublin 
canal plants, identifies the latter with the Mucruss variety : in 
this opinion I cannot concur without additional evidence in its 
support, the very different degree of roughness in the stem being 
alone a sufficient diagnostic. 
