mackay’s equisetum. 
29 
exception of the transverse septa occurring at the sheaths. In- 
stead of being uniformly simple, as represented in the figure 
at page 25, it is very frequently spar- 
ingly branched, as shown in the left 
hand figure in the margin ; the branch- 
es rise singly from below one of the 
sheaths, and a stem often bears two or 
three such branches ; the branches 
themselves also occasionally emit other 
branches in the same way, the plant, 
in that case, being very luxuriant, and 
attaining a height of three to four feet : 
the right hand figure in the margin is 
a diagram showing the mode of branch- 
ing. Under the microscope the struc- 
ture of the stem appears precisely 
identical with that of E. hyemale ; the 
double row of elevations on each of 
the ridges, with the cup-shaped depres- 
sions and stomata in the furrows, are 
exactly as I have already described 
them. The sheaths are generally black, 
the central part sometimes white, but 
scarcely ever so distinctly banded as 
in E, hyemale : the teeth are very long, 
flexuous and setiform ; their edges at 
the base are dilated, membranous, somewhat whitish, and nearly 
transparent ; they are usually, but not invariably, persistent. 
The catkin is small, nearly black, apiculate, terminal, and stri- 
ated as in the preceding species : the scales are about thirty in 
number. 
In my history of the British Equiseta published in ^ The 
Phytologist,’ I have treated this and the two following species as 
varieties of E, hyemale : abler botanists than myself, and more 
particularly Mr. Brichan, in an admirable paper in ‘ The Phy- 
tologist,’'^ have courteously but decidedly expressed their disap- 
^ See Appendix B. 
