CHARACTERS OF BRITISH PLANTS. 79 
aviculare are as different from one another, as are any forms ` 
of these two. ; 
Polygonum aviculare (Linn.)—Fruit frequently longer than 
the perianth, more particularly in a long straggling variety 
which has much the habit of the sea.side specimens of P. 
Roberti, but still with the striated fruit and other characters 
of P. aviculare. 
Rumex sanguineus (Linn.) and R. conglomeratus (Murr.)— 
It appears to my eyes that some plants are so intermediate 
between these two alleged species, as to render their proper 
name and place doubtful. The tubercles occur on one, two, 
or all the enlarged petals; the whorlsare all leafless, or leafy 
below and leafless above, or leafy throughout. 
Betula alba (Linn.) and B. glutinosa (Fries.)—Assuredly 
the specific characters assigned for these alleged species, in 
the Manual, will not suffice to distinguish them. 1 find the 
form of the fruit, and the relative length of its membranous 
margin, both varying, without any correspondence with the 
variations in the form of the leaves. I have also seen cor- 
date, ovate, and deltoid leaves on the very same tree. In 
my former paper, in the London Journal of Botany, page 
619, and more at length in the Phytologist, page 817, I have 
explained that the form of the leaves varies with age and 
luxuriance, and cannot be taken for specific characters in 
nature, though in small sprigs for the herbarium these cha- 
racters may seem clear and strong enough. 
Juncus compressus (Jacq. and J. cenosus (Bich.).—No 
certain distinetion in the length of the mucro of the capsule. 
It varies, but the shorter-capsuled shore plant sometimes 
has the mucro quite as long as that of the longer-capsuled 
freshwater plant. 
Luzula Forsteri (DC.)—Peduncles of the fruit drooping, 
not * erect;" although by no means reflexed as are those of 
L. pilosa. deis. 
Alopecurus geniculatus (Linn.) and. A. fulvus (Sm.)—The 
difference between these two species, in the relative length 
* 
